Packing a knee with ice and sending a child back into the game could lead to serious injury. Kids shouldn't play a major sport every season. Choose sports that work different muscle groups. For example, if they're long-distance running in the spring, they shouldn't play lacrosse in the summer and soccer in the fall.
Weight training is more appropriate.
Don't let children play on more than one team per sport per season. It's important for them to rest on weekends if they're playing sports during the week. See a doctor is your child is limping. A good suggestion is getting to know your child's coach. Find out whether the coach is more interested in winning or making sure children are having fun.