If you keep this from the 10-year-olds, you are sending the message to both them and your daughter that being gay is something bad that should be kept secret. No one is suggesting anyone tell 10 year olds about sex or that anyone will be making out. You should simply treat your daughter and her partner like you would treat any opposite-sex couple. Introduce the girlfriend as your daughter's girlfriend or partner and say that they love each other. That's it. If they ask questions, then you can answer them. It's really quite simple. The adults are the ones with the prejudice and who are focused on sex; not the kids. Kids of any age should be fought about love and that people can fall in love with people of any gender. To do any different is homophobic and damaging. It hurts your daughter to treat her differently and it sends the message to your other children that gay is bad. People seem to have the idea that kids shouldn't know about being gay-- but all gay people start out as gay kids. All kids should know that their parents wi love them if they turn out to be gay. And all kids should know that being gay is okay-- otherwise they will bully their gay peers at school. The way to prevent things like suicide is to teach all kids (all people) that humans come in all varieties and all the varieties are okay. Your kids should know that being gay is okay and everyone loves their sister. Otherwise they might grow up thinking that their family doesn't approve of gay people, so no wonder that tragedy happened to their gay relative.