My husband took my baby

Ok so my husband and I have been separated n we are still fighting. Everytime he comes to drop of my son he starts shit with me in front of the kids. So today my kids n I went out n we found a cell phone. It was locked so we couldn't call the owner. I told my kids will hold it until late someone calls then we can answer it n notify them so we can return it. My husnand has our 3year old. When he came home to bring the baby he saw my oldest holding the phone n he snatched it from his asking where did you get this. My son said we found it when we went out. So my husband comes to me saying why you all stole this phone ur not going to give it back. He took the phone n put it in his pocket. I told him to return the phone n leave my house he wouldn't he was like let me see what you'll do you'll call the cops go ahead. So I called the property security n they came. I told them I don't want this men near my property he is not on my lease n does not live here. I told the security he took a phone from my house it does not belong to him. The security said we can do anything about the phone but we can make he leave. So they kicked him out. He went back in the house n took my 3years old n said I'm taking my son he's not staying with you no more n he left. Then he was like "I'll see you in court bro" n laughing. I called the cops they came. I told them what happen. They told me we can not go get your son back technically your all still married n he has as equal rights as you do. I told them I don't trust him he's an unfit father, he can't take care of him but the still said I'm sorry we can't do anything. So here I am my husband took the phone we found and my kid n I feel so helpless. I've decided to let him keep the baby for a while so he can see what I have been going through. I am not going to help him with him for several weeks so he can learn his lesson. What do you all think. Any advice?