Unless your kid looks like he might have a shot at D-1; no football (well discourage him, but ultimately his decision). I remember a really talented Basketball player (who was a bean pole) playing 8th grade FB with my son (who had a TE body but O-Line speed) and I remember saying to BB player's mom that if he were my kid, no way would he be playing FB (which is what his parents thought - and ultimately what happened).
I really disagree with going to FB coach and telling them you don't want your kid doing X or Y. There was a kid on my youngest son's class who had a track offer from UCLA and that is what dad did. Kid played WR, no DB no Special teams, etc. Really was a distraction and many people knew. Turns out the track offer fell through. IMO, it did no one any good for him to be playing. No injuries, but was underutilized and a non factor in FB and there was enough grumbling amongst players and parents. Coach was a real nice guy, a good effective coach, but it probably wasn't fair to the team.
My son got small college interest (very limited FCS, mostly lower - one 3/4 scholarship). Ultimately he decided not to play any college ball. Made me a happy man. He got to have fun, got out with no injuries (he was one of the bigger, stronger players on the field) but he'd been on the small side at even the FCS level.