I'm a big MMA fan. I have a 2 and a half year old boy. I watch MMA with him around regularly. I've also trained MMA for close to a decade. He's came with me to the gym and seen my spar, as well as went to live MMA fights with me ringside as i have a friend who owns a regional MMA promotion. I don't really think its a big deal. I tell him its not ok to hit people and so far he has never been agressive towards another kid. Of course he likes to rough house play because he see's Daddy doing it. If it becomes a issue in the future i'll address it but for now i think its fine.