Children Move Less as They Get Older

Kids' activity is decreasing dramatically between 9 and 15," said study author Dr. Philip Nader, professor emeritus of pediatrics at the University of California at San Diego in La Jolla.

Nader said the reasons for the drop are many.

"There may be competing, more interesting things to do; physical education is being done away with in some places, and so is recess; there aren't as many open spaces or parks, and being outside is one of the main things that keeps people active,".