I don't which one is worse, having your son act like the 7 year old sister, or having him continue getting physically hurt by her. I would tell his father that the bruises and scratches were not there when he left and if he is so certain that the 7 year old did not hit him, then what happened? Four year old may make up some things, but never the same thing over and over, consistantly. Let the father know that you do believe your son and you are concerned for his well being: physical and emotional/psychological. Tell him how it is effecting the way your son is treating the baby and that this started after he had continued to complain of being hit by his older sister. Tell him that,at the very least, could he keep a closer eye on the two, keep them seperated when he is not in the room, something...just to at least consider the possibility that your son might be telling him the truth. He should give him the benefit of the doubt, just as he apparently does to the older sister. Also, try to explain to your son that the reason he keeps getting in trouble is because he is doing the same things to the baby as his older sister does to him. Remind him how bad it feels when he gets treated like that and let him know the baby feels the same way. Basically, he knows it is wrong for his sister to hurt him or be mean to him, so make him see that for him to do the same things is just as wrong. Sort of like, treat the baby like you wish you were treated by your older sister, not how she actually treats you. Because he is better than that. And let him know that you and he can work together to try to fix the situation with his dad and the older sister. I think that the dad is the key to getting this situation corrected, and, if you continue to try and reason with the dad long enough, he has got to at least give it some thought.