Soon after moving to a new house, my friend Lisa returned to her former digs to pick something up. As she walked in the door with her 4-month-old, the baby became visibly excited  -- she seemed to know she was in a familiar place. Chances are, it was the odor that tipped her off. "Unlike eyesight, which can take a few years to develop, smell is the most advanced sense that babies have at birth," explains Seema Csukas, M.D., director of child health promotion at Children's Healthcare of Atlanta. And tots use their sniffer mostly to stay close to you. Here's a time line of how your baby's scent sense develops:

1. Even before birth, fetuses can smell. One study found that 3-day-old infants could recognize the specific smell of their mom's amniotic fluid.

2. At birth, a newborn is drawn to the smell of breast milk; by 2 weeks, a baby can tell the difference between the scent of his mother's breast milk and another mom's milk.

3. A familiar odor can soothe your infant, a recent Swiss study found, so try holding her with a blanket that smells of breast milk or baby lotion during her next vaccination.

4. For the first two months, your baby prefers your scent to anyone else's. Even at your dirtiest, your baby still thinks you smell like roses.