The events that result in adult diseases often occur during childhood. The risk of osteoporosis later in life, for instance, is related to the amount of calcium someone receives in childhood. New evidence suggests that the risk of Alzheimer's disease correlates with head trauma during childhood (Journal of Neuropathology and Experimental Neurology 1999;58:982-992). So make sure your children's bike helmets fit well and are worn correctly. Even if head bonks don't cause noticeable brain damage now, they can set in motion a chain of events that could erase their memories in the future, when they should be enjoying their golden years.