We are not officially out to our kids yet. My kids have all met my BF. They just know him as my best friend from high school. My 16yo daughter knows that we were close and kind of dated in high school. I think she suspects but she has not said anything. She has come out to me as bi herself, although has not had any same sex relationships. She recently did an art project with various LGBT flags and she actually included the "polyamory flag" in that. I thought it was interesting.
We have had general conversations about dating more than one person (her best friend is also bi and has a boyfriend and also dated a girl last summer without breaking up with the boyfriend, all with his knowledge). She seemed bothered by that fact though, so it may prove a challenge once we do talk with her. But I am confident that as long as she knows her Dad and I are together on this she will be okay. Plus, she likes my BF a lot. Thinks he is hysterical.
We also have a 6yo girl and a 3yo girl. The youngest spends plenty of time with BF and I together and she is always excited to see him because he plays with her at the playground. The middle one is also comfortable around him, but she would be the one to out us to family just because she has no filter, like most 6 year olds. LOL
The only reason we have not told them is because my boyfriend isnt ready. His kids (teens) know mine and since his wife has asked that they dont find out, we are respecting that for now. But I am antsy to tell them, just so I can be affectionate with him when they are around. I would prefer to not hide our relationship from them since we expect he will be here for the long haul.