Children's Sense of Balance:
"From conception to the first fifteen months after birth, the vestibular system is very active as a child gains a sense of gravity and knowledge of the physical environment through movement. Every movement of the child stimulates the vestibular system, which stimulates the brain for new learning. From this sensory 'wake up' and basal understanding of gravity, a child is able to perform the most remarkable feats of balance." Smart Moves, by Carla Hannaford, pp. 35-36

What is the Vestibular System?
The vestibular system controls one's sense of movement and balance. It integrates the sensory inputs that give us information about gravity and motion, our body's muscular movements, and our body's position in space. Your baby's vestibular system is developing minute by minute and can be stimulated by movements that move her head off center. These movements might be performed by her alone (e.g. rolling), but many times they also occur while she or he is being moved by you