I’m going to be harsh here: There’s nothing you can do to change his behavior, that’s up to him. All you can do is point out the need for change, and change your own situation if he refuses.
ADHD treatment requires more than just popping a pill when you can manage to keep track of it. Mental health issues are no excuse for putting a child’s well being at risk. If he’s unwilling to properly treat his condition, that’s great and his choice; but he should not be allowed in the same building as children, since he’s shown a complete disregard for his own child’s safety.