Have you asked them if they have issues with you and the new relationship?
My husband told his children that if they had issues with he and I dating they needed to talk to us. That did not mean that they had a say in who he dated but if things are not discussed then resentment starts to build and it can make everyone’s life miserable.
Could it be possible that the ex is telling you this in an attempt to alienate you from either the children or the new relationship?
We went through this same thing also. The boys mother was telling them all sorts of things about me that were not true so that they would not want to be around me. The thing about this that she didn’t realize is that they eventually noticed that most of it wasn’t true. She even went as far as talking to my ex and telling her STBX (my husband now) things that she heard about me.
There should be no reason that the psychologist can not inform you of the same things he is telling your ex. Maybe she has asked them not to share information with you as a way of “keeping control” but you are entitled to any information about your children that your ex is, especially when it comes to their well-being and care.