Once, after coming home from the zoo with exH, before we went through the mediation, the first words out of DD4's mouth were 'Daddy's friend met us at the zoo' -- not a word about the animals, even though she adores the monkeys there and lives for the chance to see them. She was 6 at the time.
I managed to stop exH from introducing the OW as the love of his life to the DCs, from having her overnight at his place while the DCs were there, and from double dating with the DCs and the OW during visitation weekends (e.g., if the exH and the DCs were going to the zoo, then the GF would not tag along.)
ExH protested that he was entitled to have all the people he loved around him whenever he felt like it, but the mediator we had working with us told him it was in the best interests of the DCs and his relationship with them to take introduction of the GF very slowly. He had to accept my demands.
They have been to a few dinners at her place (exH and the OW don't live together; exH is actually more interested in men than women but OW probably doesn't suspect this) and despite the wide age range of all the DCs, they all know the truth about 'Daddy's Friend' and think very poorly of them both. They are especially
at the fact that exH sometimes drags them to attend the church she goes to. They are also subjected to exMIL's rhapsodies on the niceness of the GF and her DS, who is a bit older than DD1 whenever they visit exMIL.
ExH has accused them of being rude to both his mother and to the GF.
. For this I read, 'Your clear understanding of right and wrong here reminds me that I am a shit. I cannot accept that about myself, so I will accuse you of rudeness.' ExH threatened DD1 with contempt of court proceedings after their last encounter. She is a 20 year old university student and he screamed at her to get herself a lawyer.
I have never spoken to the GF, and won't until there is a ring on her finger, but that is not likely to happen.