if their is no custody order, can the mother sign children out of school where father lives n sign them into school near her?

For the past month my ex boyfriend has told me not to come see my children.I do not live with him. He lives in seaford with his girlfriend. He verbally abuses me in front of my children when I do go n see them. Sometimes physically coming at me. The mental n emotional abuse I get from him is so much to bare that I get panic attacks. I want to take my children but he said I can't n so did the cop because they reside their with him.he said my ex that I can see them when he says its OK. I'm heartbroken inside. I don't know what to do? I need to know what I can. Please please give me advice. I live in Medford NY area.