This one requires the backstory which is on my post here: https://www.mumsnet.com/Talk/amiibeingunreasonable/2961751-how-the-hell-to-explain-to-dc-why-i-m-withholding-contact
As per that thread, DC contact with ex has resumed following his short term assurance his GF won't be around them. We are in court in 2 weeks for a hearing of my application of a prohibited steps order.
I noticed that recently my eldest DC was taking herself off and closing doors at points in her phone conversations with her father. She did it last night and I casually enquired why - stressing that I didn't mind but it was unusual behaviour.
She burst into hysterical tears and told me her dad had been putting GF on the phone to talk to her. She said he initiated this, she didn't ask. She told me he had told her to keep this from me. She then said he had been talking to her about GF and how much she missed them and liked them and 'would never hurt them' and had given her a notebook to write her feelings down in so he could show CAFCASS her thoughts (presumably on how she wants to see GF again). She is very young for her age and impressionable and her analysis of the situation is that GF is nice because she bought DD a Beauty and the Beast sticker book.
I cannot imagine that CAFCASS have asked him to do this as no mention was made to me by them of garnering the DC's feelings in the situation as it is a complex safeguarding issue that I don't feel they can fully understand. Surely they would not have asked their father to gather 'evidence' in this way without telling me or making other arrangements to consult the children?
Poor DD is really confused and upset by it all and worried about having told me things when her dad told her not to but said she didn't want to lie to me 
Does anyone have experience of CAFCASS using this tactic? Obviously I can't contact them until tomorrow. This is actually starting to feel like he is attempting parental alienation, and telling my children that I'm being mean and unreasonable. I don't feel it's in DD's best interests to develop a deeper bond with this woman when Social Services have supported my viewpoint that she shouldn't be around my children, and I fee he is manipulating her naivety to strengthen his own position with the courts. How on earth do I tackle this???