All About Your 4-Month-Old Baby's Milestones and Development

From physical milestones to language and beyond.

If it feels like your 4-month-old is a whole new baby at times, you’re not imagining things. The 4-month mark is a big milestone in your little one’s life, thanks to some major brain and physical development milestones. Most babies by this age will have doubled their birth weight (or weigh more) and will be sleeping longer stretches at night.

Being 4 months old comes with so many new, exciting achievements. From improved mobility to a more consistent sleep schedule and interest in solid foods, the developmental milestones at this age happen quickly—so it's important to keep up! Ahead, learn more about your 4-month-old baby's milestones, from physical to language and beyond.

At This Age

  • Development: Your baby's vision is improving, they are becoming more sociable, and are beginning to reach and roll.
  • Sleep: Your baby is likely taking three to four naps a day. The dreaded 4-month sleep regression may make an appearance.
  • Food: Your baby is still getting plenty of breastmilk and/or formula every three to four hours.
illustration of a baby, text reading 4 month old

Joshua Seong

4-Month-Old Baby Physical and Cognitive Milestones

Your 4-month-old baby is really starting to come out of their shell! You're likely noticing their budding personality and improved physical abilities. Ahead are some physical and cognitive milestones to watch out for at this age.

At 4 months old, your baby has likely doubled their birth weight. Babies this age typically gain about 1 to 1¼ pounds and grow about 0.5 inches per month.

Vision

Your baby's developing vision allows them to track objects, and their increased neck strength helps them hold their head steady. They are able to sit upright with support and are able to follow moving things with their eyes from side to side. They also enjoy looking at more colors, shapes, and patterns.

Language and Recognition

Your baby's brain is also developing rapidly. "So many connections are made in your baby's brain during this time," says Florencia Segura, MD, FAAP, a pediatrician at Einstein Pediatrics in Vienna, Virginia. "These brain connections are being reinforced through a concept known as 'serve and return.' When your baby 'serves' you language by a smile, laugh, or coo, the parent 'returns' it with a smile, laugh, or acknowledgment."

What's more, your baby recognizes familiar faces now! They are likely giving you (and other prominent family members and/or friends) a big smile when you walk into the room. They can also mimic certain facial expressions or sounds and respond to affection. You might even get that coveted first laugh.

Reaching and Exploring

Additionally, 4-month-olds love to shake objects and bring them to their mouths. They are also likely to become fascinated with their feet at this age. You may notice that they are reaching for just about everything! This is because they are coordinating vision with movement—meaning that when they spot something they want, they are going to make a break for it.

Muscle Development

Your baby should also be able to push up onto their elbows or hands during tummy time. They may even start rolling from belly to back and should be able to push down with their legs as you help them stand up on a flat surface. (This is a great way to build leg strength!)

Additional Behaviors at 4 Months

  • More interest in playing with people
  • Reaches for objects with one hand
  • Swings at dangling toys
  • Smiles spontaneously
  • Notices their reflection in the mirror
  • Bears weight when standing on a hard surface

4-Month-Old Baby Food Milestones

While breastmilk or formula is all your baby needs at this age, you can also introduce solid foods between 4 and 6 months, as long as you get the OK from a pediatrician or health care provider. Once you are given the green light, it's best to start with soft foods that they can mash with their gums, such as baby cereal. Introduce them one at a time and monitor for any allergic reactions. However, keep in mind that the Centers for Disease Control and Prevention (CDC) does not recommend starting food before 4 months.

Many pediatricians advise baby-led feeding, which encourages parents to follow their own baby’s cues to know when the best time is to introduce solids. Some babies may be ready to try solid foods earlier (around 4 months) and some babies may not be ready until closer to 6 months. Every baby is different and it's important to avoid introducing solids too early.

According to the American Academy of Pediatrics (AAP), here are some signs your little one may be ready to start solid foods:

  • Holds their head up
  • Opens their mouth near food
  • Tries to move food from a spoon to their mouth
  • Has grown big enough (at least doubled their birth weight)

Please also keep in mind that it's best to have children try one single-ingredient food at a time, which helps determine whether your child has any food sensitivities or allergies.

4-Month-Old Baby Sleep Milestones

In general, your 4-month-old needs 12 to 16 hours of sleep per day. "During the day, they will be taking four naps totaling an average of three to four hours of daytime sleep," says Dr. Segura. "The wake windows between these naps are between 1.5 to 2.5 hours."

Your baby may be getting a little older, but all of the same safe sleep practices still apply. "It is recommended that babies sleep in their own bassinet or crib in a parents' room [for] up to 6 months minimum," explains Lyndsey Garbi, MD, chief pediatrician of Blueberry Pediatrics and a member of the Parents review board.

If your baby has started rolling from their back to their tummy, Dr. Segura adds that it is okay for them to do so at night while they are sleeping. However, it is still important to place them in their crib on their back.

4-Month-Old Baby Sleep Regression

The dreaded 4-month sleep regression is likely to pop up at this time. All of a sudden, your expert sleeper is waking up at all hours of the night for reasons you can't quite figure out. It is certainly frustrating, but remember, you're not alone! This too is a phase that will pass.

Often, sleep regressions are the result of a “growth spurt” in your baby’s brain and body. This is temporary, so continue to be consistent with your baby’s routine and sleep patterns.

Some helpful sleep habits to keep in mind at this age include laying your baby down awake but sleepy. As your little one learns more about cause-and-effect this month, they may soon realize that by crying, their parents will come to pick them up. You might have to experiment more this month by teaching your infant to self-soothe or fall asleep on their own.

You can also allow pacifier use for naps and bedtime. The AAP still recommends pacifier use with naps and bedtime as it is associated with a reduced risk of SIDS.

4-Month-Old Health and Safety

It's time for your baby's 4-month well visit! At this appointment, they will receive all of the same vaccines they received at the 2-month visit. These include second doses of the pneumococcal, DTaP, Hib, polio, and rotavirus vaccines.

Along with the physical examination at your 4-month well visit, a health care provider will discuss your baby's feeding and sleep schedule, how your baby is growing, and any concerns you might have.

Sleep Safety

At this age, you should still be following AAP guidelines for preventing sudden infant death syndrome (SIDS). Babies should sleep on their backs on a flat surface without any toys, pillows, blankets, loose bedding, or bumper pads to avoid suffocation. Your 4-month-old should only be brought into your bed for comfort or feeding, as the AAP does not recommend bed-sharing for any baby.

Car Seat and Home Safety

Dr. Garbi explains that your 4-month-old should continue to stay in a rear-facing car seat that is securely fastened, and to avoid wearing jackets while in the seat. She also recommends you start babyproofing your home in preparation for them becoming more mobile in the next few months. This includes adding childproof locks where needed, covering sharp edges on furniture, and covering electrical sockets.

Colds and Runny Noses

Many babies can have runny noses with green or yellow discharge, but not have an actual sinus infection. Green-colored discharge might just indicate the body is doing its normal function of clearing the sinus and nasal passages. However, if your baby’s cold lasts longer than 10 to 14 days or has severe symptoms accompanying it, such as lethargy or dehydration, you should take them to a pediatrician or health care provider for assessment.

Stomach Bugs and/or Vomiting

If your infant is exclusively breastfed, the best thing you can do for them through a stomach bug that causes vomiting is to continue to try to breastfeed. Breast milk is more easily digestible by babies than electrolyte replacement drinks such as Pedialyte, so breast milk is preferred in any illness with an infant.

If your infant vomits after nursing, try shortening the nursing session to five or 10 minutes and waiting a few hours to see if the baby can keep the feeding down. If your baby is not able to nurse or vomits everything up after 24 hours, you should seek medical attention.

For formula-fed babies, you can offer 0.5 to 1 ounce of oral rehydration solution in a bottle or syringe, such as Pedialyte, every 15 minutes for two or three hours. If vomiting occurs, wait 30 minutes and try again. If your baby is able to keep the solution down, you can resume normal formula feeding.

Fever

If your baby develops a fever up to or higher than 102 degrees F, you should contact a health care provider. If your infant has a fever that rises above 104 degrees repeatedly, you should seek medical assistance right away. If their fever persists for more than 24 hours, or they are still acting sick after the fever is brought down, you should also call their provider. For questions concerning infant Tylenol, also reach to to a health care provider.

Thrush

If your baby has white patches on the inside of their mouth or tongue, or develops a diaper rash that appears symmetrical and will not go away with diaper rash cream treatment, it might be thrush. Your baby's pediatrician can evaluate them for thrush and may provide an oral medicine for the mouth or an antifungal cream for diaper area infections.

4-Month-Old Baby Care Basics

Here are some basic care tips for your 4-month-old.

Burping Your Baby

While burping your baby is important, they might not need to burp with every single feeding at this age. As your baby is able to sit up more and hold their head up better, they may be able to tolerate feedings without burping multiple times now. Every baby is different though, so if your little one seems uncomfortable or gassy, continue burping after feedings.

Preventing Bug Bites

Most insect repellents are safe to use on your baby once they are 2 months old. If you and your little one are outside often, exercise caution and do your best to protect your baby naturally by using products with natural ingredients and avoiding buggy areas like under trees or other foliage. Mosquito nets are another option. For additional questions regarding insect repellents, be sure to reach out to a health care provider.

Sun Safety

Since babies younger than 6 months old should not wear sunscreen, it's best to avoid direct sunlight. Try staying in the shade whenever possible, and limit sun exposure during the peak daylight hours between 10 a.m. and 4 p.m. If they do have to be exposed to the sun, make sure to dress them in protective clothing, including sun hats.

Avoiding Honey

Babies younger than 12 months should never be given honey. This is due to the rare but serious risk of botulism, which can cause abnormal functioning of the nerves, leading to weakness and paralysis.

4-Month-Old Baby Schedule and Activities

In between naps and feedings, your baby is spending a lot of time exploring on their tummy. There are a variety of tummy time toys to help facilitate their cognitive, physical, and social development, including rattles, mirrors, musical instruments, sensory toys, and activity gyms. Soft blocks and books are also beneficial. Put your baby down on the floor or play mat, place a few toys in front of them, and encourage them to reach for the toys.

As you're hanging out, you can help your infant’s development by using a baby seat, holding them on your lap, or using a breastfeeding pillow propped behind them as they learn to sit. Of course, never leave your baby unsupervised near a pillow, especially as they develop those muscles needed to hold themselves up, because there will be a bit of toppling over that happens in the beginning!

Along with their growing interest in playtime, they may also begin to grow new teeth. Teething toys are incredibly helpful in soothing sore gums and crankiness. Your 4-month-old's schedule should also include a bedtime routine—it's the perfect time to start if you haven't yet. You can try a warm bath, some soothing cuddles, or a couple of songs.

When to Contact a Health Care Provider

If you notice your 4-month-old exhibiting any of the following behaviors, it's best to bring it up to a pediatrician or health care provider:

  • Does not respond to or seem interested in your face
  • Does not smile
  • Has crossed eyes
  • Unable to hold their head up or sit with support
  • Does not watch people or items as they move
  • Has gained less than 50% of their birth weight

Remember that every baby is unique. Babies reach different milestones at their own pace, and a health care professional will be able to assess your child's progress.

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Sources
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