Your baby's body is equipped with survival reflexes, and one of the most important at four months is that everything goes in the mouth. This is how they explore the world — the inside of their mouth is still the most familiar means of interacting with their environment. It is completely normal, developmentally appropriate, and important.

What you can do: Offer safe, clean teething toys of different textures and shapes. Allow mouthing of appropriate objects — this is not something to discourage.

Gross motor development builds progressively through the first year. The strength and coordination your baby is developing right now through tummy time, reflexive movement, and daily activity is laying the foundation for crawling, standing, and walking ahead.

Your four-month-old is beginning to learn how to control their arms and legs. They will most likely be starting to reach for things intentionally. You can help them figure out how to do it by guiding their hand toward the object they're trying to reach — this teaches the movement pattern their brain is working to establish.

What you can do: Hold toys just within reach and let them work toward grasping them. Guide their hand gently if they're close but struggling.

Balance and coordination milestones begin to emerge from Month 6 with sitting. The foundations are being built through tummy time and reflexive movement right now.

Your four-month-old baby now likely has a very clear mental template for the human face. That means they can recognize the pattern of a face wherever they see it and are getting better at learning new faces — recognizing not only yours but those of others who are often in their field of view. They'll be interested in new faces, though they may not respond to them as favourably as to yours.

What you can do: Introduce your baby to trusted family members and friends. Each new face is a new data point in their growing understanding of the social world.

Imaginative and creative development begins to emerge around 12–18 months. Right now, your baby is building the sensory and cognitive foundations that will support creativity later.

Problem solving emerges and deepens progressively through the first year. The neural pathways for thinking, planning, and cause-and-effect understanding are being laid right now through every sensory experience and interaction your baby has.

Early academic foundations — language, numeracy, and literacy awareness — begin to develop from Month 9. For now, every word you speak and every face you show is building the cognitive architecture for future learning.

Social sharing and cooperation emerge from Month 6. Right now, the most important social development is the bond forming between your baby and their primary caregivers.

As baby exerts more control over their limbs, they're also learning to control their voice. They've started to experiment with the different sorts of sounds they can make, as well as playing with tone. They've even started to babble, using sounds that approximate the syllables they hear you use when talking.

What you can do: Talk back to every vocalization. Repeat the sounds they make. Change your pitch and rhythm. This is a musical, conversational dance that builds language.

Your little one's personality is really starting to emerge. At four months, they've started to use their whole body to communicate how they're feeling — especially when feeling good! They wriggle and squeal when they find something delightful. They may laugh when something you do strikes them as funny.

What you can do: Respond to every expression of delight with matching energy. Your enthusiastic response teaches them that emotions are worth expressing.

Security and happiness are built through consistent, responsive caregiving in the early months. Every time you respond to your baby's cries, you are building the secure attachment that underpins all future emotional development.