What do mean by tackle football is that rugby or american football?
Let him play what he wants to play, accidents happen in contact sports that's how it is.
Don't pull him out of football because your worried about him, worrying is a waste of emotion when he's older he will make up his own mind if its worth playing a contact sport.
When I was in 11 I played rugby an most of the guys I played with then stopped playing by the time they hit high school most probably because they realized it wasn't worth it for them an or they realized they could get hurt or whatever.
Let him play what he wants to play let him decide if it's worth playing or not after his concussion if he still wants to play it shows he really loves football so let that tell you somethng.