Abusive ex...

So my ex was very abusive when we were together. Physically and mentally.. And we have two kids together. Our daughter was pretty young when it happened so she doesn’t know much. And she obviously doesn’t know how he talks to me now. She’s almost 7 and such a daddy’s girl and I haven’t told her about what kind of guy he was/is since I feel like she’s too young... My friend told me I need to tell her how he was abusive to me and I’m not sure if she’s old enough to know yet.. They don’t get to see him since he’s always high and I don’t think they’re safe with him.. But should I tell her about his abuse and his drug use? She thinks I’m just being mean to him but I’m just protecting her and her brother from him.