You may be interested in my post about when my nephew sprung his "DO you have two husbands?" question on me - here
in my Notebook blog (and reading GG's reply there).
Our friends' kids don't seem to notice that we have an "extra" as at friend-type functions there are always extraneous adults, but at family-type functions it's a bit more obvious that the friend/family line is being crossed.
I would definitely let the kids parents take the lead...since you are out with them (we are not out to my family per se
) you could ask them how they would like to present things...as long as it doesn't directly conflict with your values you could choose to just back what they choose to say.
Just my thoughts.