I've written about this at length in my personal blog.
We have 4 kids. Ages 5, 12, 16, 20. and a grandson age 1.5
We've been honest and upfront with them and they all know where to find me if they need me (certain times in Maca's bedroom, others in GG's bedroom).
We are also upfront and open with our extended family. The ones who had a problem with it were given the option of keeping their opinions to themselves or departing our lives-end of subject.
It's VERY hard on kids to have adults who treat other meaningful adults in their lives with disdain.
I love my dad-but that's why he is no longer a part of my life. His and his wife's malice towards GG (boyfriend) was so upsetting and concerning to our youngest (who was 3 at the time) that she is STILL traumatized and there was only ONE WEEK that she was around all of them and aware of an issue.
On the upside, we introduced GG as our roommate, nanny, uncle-over the years to the schools-and have had no issue there.
As for other kids-again, no issues. Other kids come over all of the time and even stay the night.
"Love As Thou Wilt"