Your 12-week-old baby is no longer a tiny newborn. She has quickly grown into an active infant who responds to you and her surroundings. She is losing some of her involuntary newborn reflexes and gaining more control of her body movements. According to MedlinePlus, a service of the National Institutes of Health, your baby's physical development starts at the head, then progresses to other areas of the body. For example, she will learn to suck before she sits, and she will sit before she walks.
Around 12 weeks of age, your baby will become fascinated with his hands. Expect him to examine his fingers and thumbs closely, put them in his mouth and try to suck on them. Your baby will probably smile now when he hears your voice. He pays very close attention to people's faces, gazing at them intently. He now recognizes familiar things and people, and his eyes follow moving objects. By 12 weeks of age, your baby should begin to show some hand-eye coordination, and he may turn his head in the direction of sound.
Your baby should begin to babble and imitate sounds around 12 weeks of age. She may squeal, coo and blow bubbles. You can help your baby with early language development by talking to her extensively and by reading to her. It doesn't matter so much what you talk to her about or what books you read. Your baby just needs to hear a variety of words and learn about the rhythm of your voice.
At about 12 weeks of age, your baby will likely be able to hold her head up for a few moments while lying on her back. When she's lying on her stomach, she may lift her head and chest, and she may even roll over from her stomach to her back. She can shake and grasp things, and she may bat or attempt to grab dangling toys. When you place her feet on the floor or other firm surface, she will push down and put her weight on her legs. When lying down, your baby will kick and stretch out her legs.
All babies are different, and they develop at different ages. Although most babies reach certain milestones at approximately the same age, the March of Dimes advises that it is not unusual for a perfectly normal, healthy baby to develop faster in some areas and slower in others. Use milestones as guidelines, and talk to your baby's doctor about any concerns.
According to MayoClinic.com, you should consult your baby's doctor if, by 12 weeks of age, your baby has shown no improvement in head control, does not try to lift his head when lying on his stomach, or if he displays extreme floppiness. Other causes for concern include failure to gain weight, no response to bright lights or loud noises and failure to focus on his caregiver's eyes.