Vigorous exercise can lead to better sleep in kids. According to a study in Germany which involved 11 kids with a mean age of 12 years, who performed 2 bicycle exercise sessions (one of medium intensity and one of high intensity) on 2 different days, revealed that high intensity (vigorous) exercise was associate with a shorter sleep latency, more deep sleep and greater sleep efficiency. The results suggest that the intensity of exercise may be the important factor in the sleep effects of exercise seen in children.
Sleep Medicine vol 9 (3);pp 266-272 March 2008