Milestones reached in a baby's first year include the first real smile, rolling over, sleeping through the night and the emergence of a tooth. These and other milestones follow a loose timeline that helps parents discern if their baby is on track with her peers or an early or late developer.
A smile is a baby's first social skill and occurs somewhere around 8 weeks old. At that age, a baby's vision and nervous system are developed enough to smile a real smile as opposed to a smile caused by gas. Rolling over occurs around 2- to 3- months of age and happens when a baby is strong enough to lift herself to a push-up position and roll from front to back. Rolling from back to front takes more strength and coordination and happens later, around 5 months old.
A number of factors affect when a baby sleeps through the night, including a decreased startle effect, increased weight gain, decreased multiple night-time feedings and an increased ability to self-soothe. These factors come together sometime after 6 months. A majority of babies grow a first tooth between 4 and 7 months old, although an early developer may sprout one at 3 months and a late bloomer after 1 year. Other milestones a baby usually reaches in the first year are sitting up on her own, playing peek-a-boo, grasping objects and crawling.