Why is he bringing his kids to work? Is he a single father with no reliable child-care? Is his wife sick? There could be a lot of reasons he brings his kids, and why he may not be able to supervise them properly. BTW it’s unusual for a guy to be bringing his kids to work. Usually it’s a single mother who’s having trouble with childcare.
Find out first. Then (if he’s not your boss) bring the matter up tactfully. And if he needs help, maybe offer to try to help him get it.