Baby mamma took away kids from a good father?

Krista
A few weeks ago my boyfriend's baby mamma told him we can't see his kids anymore. He is a REALLY great father. He is their coach for sports and does everything with him every chance he gets. His ex recently found out about me and our relationship because we just moved in together and she is being a jealous ex. She is a therapist so you would think she would know that revoking his privileges to see the kids will hurt them more than him. I've tried to talk to her and be nice and say I understand if you aren't comfortable with me around ur kids because you don't know me, let's have lunch and she's like oh ya forsure. Then goes and bashes me and talks shit about me to my boyfriend, stuff she dosent even know she's just talking shit. She obviously has her own issues and insecurities but idk what to do because I love those kids like my own and it's killing my boyfriend