Tee hee! A little. When two males were kissing on Masterpiece Theater, my 5 year old asked of some men kiss. What could I say? No? They were doing it.
It hasn't gotten more detailed than that yet.
I plan on just telling it like it is. There are men who like men and women who like women the same way there are men who like women and women who like men. Always have been. Always will be. Everyone is how they were born and everyone is equally valuable and lovable, and people who say mean things about "gay" people are being immature and cruel. We have close gay family friends, including my best friend, who they are already close to, so as they learn and grow we can say, "So and so is gay and we love them right?"
I don't think an issue needs to made over a basic human reality other than to point out that those who make an issue of it are choosing to do that.
They have overheard us saying things are "gay" as in silly, but maybe we should knock that off until they are old enough to realize that it really isn't a negative slam to us. Also we don't want them to use it as kids in a negative way. Although, that was so fun as a kid to run around saying "You're gay! BA HA HA I MEANT HAPPY"
What's going to be harder is explaining why our entire fundamentalist christian side of the family makes such a huge issue of it and brings it up heatedly all the time in the context of these "people" (whom they've never met) threatening American families (huh? I've never felt threatened) going to hell. Much more zealously than for any of the other millions of sins in the Bible which EVERYONE on earth is guilty of. I'm totally preparing to guard my kids from the "BEING GAY IS EVIL" speeches they're bound to hear from certain relatives. Some of which have children out of wedlock. gasp.