you can have him wear a mouth guard when he starts doing it.. when he's older they will advise for you to tell him to put his tongue to the roof of his mouth. It's just as bad for him as it is for you.. I would do the mouth guard and maybe you can stop it..
You really can't get them to stop. The thing that sucks is, it goes into adulthood and like for me, I've gritted my teeth since I was a kid and once I hit 35, I started having MAJOR jaw pain and now have to wear an appliance during the day AND night so my jaw doesn't hurt.