GUIDE
Your baby is more fun than ever. Sleep might have just imploded. Both things are happening at once.
Four months is a delightful contradiction — giggling, grabbing, squealing with excitement, and developing a personality that makes you realize you'd do anything for this tiny person. Also, sleep might have just fallen apart. Welcome to four months.
Four months is a physical milestone bonanza. Rolling is on the horizon — many babies roll from tummy to back between 3–5 months. You'll see the precursors: rocking side to side during tummy time, lifting one side of their body. Tummy time has transformed from face-planting and screaming to pushing up on forearms, and some can push up on extended arms.
Reaching and grasping are becoming purposeful — "I see it, I want it, I'm getting it." They'll grab toys, your hair, your glasses, anything within reach. Everything goes in the mouth — their mouth has more nerve endings than their fingers, so mouthing is actually sophisticated sensory exploration. According to Pathways.org, this push-up ability is a key motor milestone that prepares the body for later crawling.
The CDC's 2022 milestones for 4 months include reaching for toys, looking at hands with interest, and using both hands to hold a toy.
Cause and effect is solid. Your baby shakes a rattle to hear the sound, kicks a play gym to make toys bounce, and coos loudly because they've learned it gets your attention. Object tracking is sophisticated — they can follow an object that moves quickly and anticipate where it's going. Early problem-solving appears: some four-month-olds will pull a blanket away to find a partially hidden toy.
Socially, your baby is becoming a little extrovert. They initiate social contact — cooing at you until you look over, smiling at strangers until they get a smile back. Mirror play is fascinating — they're captivated by this responsive "other baby" who smiles when they smile. According to Zero to Three, their emotional range is expanding: joy, frustration, boredom, excitement, and displeasure with increasing clarity.
Babbling is diversifying beyond coos — squeals, growls, raspberries, extended vowel experiments. Every raspberry and every squeal is your baby calibrating the motor control that will eventually produce words. Laughter may arrive this month, and it will be wildly contagious.
Feeding at four months is usually well established. Most babies eat 5–6 times per day. Some pediatricians begin discussing solids around 4–6 months, though the AAP says most babies don't need solids before 6 months. Signs of readiness: sitting with support, good head control, interest in your food, tongue-thrust reflex fading.
The 4-month sleep regression is one of the most well-known developmental events. Your baby's sleep cycles are maturing from simple newborn patterns to complex adult-like patterns. Signs: a baby who was sleeping well suddenly wakes every 1–2 hours, has trouble falling back asleep, resists naps. It typically lasts 2–6 weeks.
If you're tracking sleep, you'll see the regression clearly in the data — and you'll also see when it starts to resolve. tinylog's sleep tracking makes this easy — log sleep with one tap and let the trends tell the story.
It doesn't feel like it at 3 AM, but your baby's brain is maturing. Their sleep architecture is becoming more adult-like, with distinct sleep stages including lighter sleep phases. This is permanent brain development — sleep will reorganize around this new architecture.
Four-month-olds are so interested in the world that they can't focus on eating. Every sound, every movement causes them to pop off the breast or push away the bottle. Feeding in a quiet, dim room can help, but it's also just a phase you ride out.
While the average first tooth appears around 6 months, some babies start the teething process at four months. More drooling, chewing on everything, and possibly some gum swelling. But drooling alone doesn't confirm teething.
The 4-month well-child visit includes growth, development, and another round of vaccines. Early identification of developmental differences matters.
