In her first four months, your baby established the muscle control she needed to move both her eyes and her head so she could follow interesting objects. Now she’ll take on an even greater challenge: sitting up. She’ll accomplish this in small steps as her back and neck muscles gradually strengthen and she develops better balance in her trunk, head, and neck. First she’ll learn to raise her head and hold it up while lying on her stomach. You can encourage this by placing her on her stomach and extending her arms forward; then hold a rattle or other attractive toy in front of her to get her attention and coax her to hold her head up and look at you. This also is a good way to check her hearing and vision.
Once she’s able to lift her head, your baby will start pushing up on her arms and arching her back to lift her chest. This strengthens her upper body so she can remain steady and upright when sitting. At the same time she may rock on her stomach, kick her legs, and “swim” with her arms. These abilities, which usually appear at about five months, are necessary for rolling over and crawling. By the end of this period, she’ll probably be able to roll over in both directions, although babies normally vary in the age when they’re able to do so. Most children roll first from the stomach to the back and later in the opposite direction, although doing it in the opposite sequence is perfectly normal.
Once your baby is strong enough to raise her chest, you can help her practice sitting up. Hold her up or support her back with pillows or a couch corner as she learns to balance herself. Soon she’ll learn to “tripod,” leaning forward as she extends her arms to balance her upper body. Bright, interesting toys placed in front of her will give her something to focus on as she gains her balance. It will be some time before she can maneuver herself into a sitting posture without your assistance, but by six to eight months, if you position her upright, she’ll be able to remain sitting without leaning forward on her arms. Then she can discover all the wonderful things that can be done with her hands as she views the world from this new vantage point.
By the fourth month, your baby can easily bring interesting objects to her mouth. During her next four months, she’ll begin to use her fingers and thumbs together in a mitten or clawlike grip or raking motion, and she’ll manage to pick up many things. She won’t develop the pincer grasp using her index finger and thumb until she’s about nine months old, but by the sixth to eighth month, she’ll learn how to transfer objects from hand to hand, turn them from side to side, and twist them upside down.
As her physical coordination improves, your baby will discover parts of her body that she never knew existed. Lying on her back, she can now grab her feet and toes and bring them to her mouth. While being diapered, she may reach down to touch her genitals. When sitting up, she may slap her knee or thigh. Through these explorations she’ll discover many new and interesting sensations. She’ll also start to understand the function of each body part. For example, when you place her newly found feet on the floor, she may first curl her toes and stroke the carpet or wood surface, but soon she’ll discover she can use her feet and legs to practice “walking” or just to bounce up and down. Watch out! These are all preparations for the next major milestones: crawling and standing.