Thank you ForeverDad. The book sounds helpful, does it mention BPD? We don't have any diagnosis, I'm sure it would be helpful regardless. Lately I have really seen how his behavior affects them. He can be fine for long periods, and it gets bad when he smokes marijuana. He will go months not touching it, and things are great, and months using it, where he becomes short tempered, entitled, manipulative and arrogant. Honestly I've come to realize what a low standard I've been having for "things are great", it's really not that great and there is still emotional abuse.
I went through a lot of this.
In my case, the advice I received (I feel like I'm sharing this a lot lately) was to validate a child's feelings and perception, but not to badmouth the other parent. And, this is important, to help them realize they can have their own thoughts and feelings separately from mom or dad (whoever is BPD). It can be difficult sometimes, because pwBPD just do not do themselves any favors in terms of how they behave toward those closest to them. I think it's okay to say how someone behaved is inappropriate, but you don't have to go as far as labeling them something. I think that might be one rule: criticize the parent's behavior, but not the parent (at least not yet).
In time, as they get older, they might ask for more information, as they see how other adults behave and realize how out-of-line the BPD parent is.
