Milk, if consumed in a short period of time, can help prevent cavities for all ages!  Milk is rich in calcium, and phosphorus.  High pH and high levels of calcium and phosphorus prevent demineralization of the tooth enamel as seen during the development of tooth decay. 

However, the milk sugar (lactose) can cause decay if left on the tooth for a prolonged length of time, especially in a baby bottle at night.   Instead, substitute water in the bottle if your baby needs the bottle to sleep.