Thanks for such a thorough, thoughtful answer!
I know what you mean about worrying about the children experiencing referred homophobia. How old are your kids? My DD has had a little bit of it at school (very carefully handled by school), and it is sad. There's also a lot of the clumsy, but actually rather damaging 'ooh goodness I didn't know which mum to approach for a playdate so, erm, we didn't invite your DD' kind of stuff. Do you find that?
I think I am more of a cynic than you about 'well-meaning straight people'. I do know some people genuinely think there's no homophobia any more, of course. But I also think there's been a backlash, and people who claim that homophobia is over really mean 'I wish the gays would stop making a fuss; it's only really rarely that someone's actually beaten up for being gay, so you have it good'.
That's terribly sad about how you learned the word 'lesbian'. 
So interesting what you say about your children! It's a closed book to me because we only have one child, so we've never dealt with the same situation. My DD is my partner's biological child. She's my world and I find it hard to imagine having a biological child and it being different.