Note: All weights and lengths are approximate; each baby is unique. These figures are just general ranges.
Communication and social development
At four months old, baby is ever more interested in his environment. His repertoire of facial expressions grows and he begins to develop a sense of humor. He’ll make a variety of noises. He greets beloved family and caregivers with a smile, and he is not yet afraid of strangers.
Senses and motor skills
Baby enjoys putting things in his mouth to feel them. In fact, his mouth is his main instrument of exploration – so make sure he has safe, developmentally appropriate toys around him. Although baby can’t pick up toys by himself yet, he does try to get closer to things he finds interesting by stretching forward and making rudimentary rolling and crawling movements. All of his senses are now fully developed.
Interests and activities
Fingers are a great delicacy to a four-month-old: He’ll put them (along with anything he may be holding) in his mouth and investigate them with great concentration. Music is another source of enjoyment: both passive and active listening, such as when a caregiver dances with baby or rocks him rhythmically. Sitting on a parent’s lap and looking around is one of his favorite activities. Many babies will shout with joy if you play “airplane” with them, swinging them on their stomachs through the air.