Physical abuse should be easy to prove. If the kids will speak up it's a clincher. Have you seen a forensic psych? Doc proof of abuse, report & testimony from psych, motion for supervised visitation, possibly compel him for counseling if he wants to see them again. I can only imagine how terrifying a huge angry man must be to a small child. Have you motioned for RO? Why have you letting this go on? Knowing this IMO I would politely tell him the FOC story while you get your case in order. I would make other appointments for the kids during this summer and insist that less than 30 day notice of summer vacation requests is unreasonable, in mid July of course.