i can't help you, but i commend you for giving this thought first.
my stbx and his gf (she's also still married), committed adultery, he moved her and her 3 kids into the only home my children knew, and now the gf is pregnant. and nobody is even divorced. my children live with me primarily and will usually talk to me about anything, even things they don't like about going to their dad's. they have known about the new baby for a month and have yet to say a word to me about it. i think that says something...that maybe they don't want to talk about it. i don't know. i know it's not advice, just my experience, which obviously my whole situation is different than yours.
but, again, kudos to you for thinking about your children. i hope everything works out for you.
kat
-------------------- What you reap is what you sow and so it goes...