Is it permissible to allow children who practice sports to participate [in activities] while wearing shorts that reveal their thighs?

If the children are young and have not reached puberty, there is no harm in them playing in short shorts. However, if they have reached puberty, it is not permissible to look at them or interact with them while their awrahs are uncovered, because a man's awrah is what is between the navel and the knee.