I often think about this as well. Our son also plays HS Football. It's his choice. He loves it.
When he stops loving it is when I will step in as his Father.
The best part of it all is that he is HEALTHY. Not just "working out", but he's part of something.
We've told our children you can play any sport you want, but you HAVE to play a sport.
I don't care what sport it is, it just has to involve physical activity.
One piece of advice I received from a friend was to remember that:
"When asked what the toughest part of playing a sport was, it was the car ride home after the game"
Be positive, constructive, ask questions, but most important, be there for your kids and show them how to play pinball.