This is the second part of my first question Is this weird or i'm i overreacting?

You should NOT dismiss your instincts...if you feel that there is something not 'right' about the relationship between he and your kids, then PLEASE keep yourself on the defensive and do not give him the opportunity to harm them. Keep your kids in your sight at all times-never leave him alone with him-and talk to them often and bee on the lookout for any behavioral changes.