Ideally, preschoolers shouldn't be inactive for more than an hour a day, according to Jane Clark, department chair of kinesiology at the University of Maryland in College Park. Movement and play are critical to their motor development (muscular coordination that's needed for refined motion), and they're just as important to the learning process as cognitive activities. At this age, the two should be combined; for instance, when giving a lesson on colors, a teacher might ask all the kids wearing blue or red to hop in place or stretch their arms to the ceiling.
But with a greater push these days on academic achievement, experts are concerned that even young kids are getting less exercise than they need.
What types of activity are best for 3- to 5-year-olds? Stretching, tumbling, running and stopping quickly, games that teach a child to move around without bumping into others, and those that tap into their imagination (pretending they're falling leaves or snowflakes, for instance). What to skip? Competitive play and strength training.