Children play hard, but they also need to rest. According to this article, they are not "little adults". 7 and 8 year old children should not train for sports more than 3 times a week and not increase exercise more than 10% a week. Parents should recognize the effects of too much training when fatigue begins to set in or school performance begins to drop. Children need to rest not only physically but also mentally.
Click here to read about the proper way to encourge children to exercise and train for their sport. The benefits are huge if done the right way.