Children need to be taught more about sex in general. Going through childhood seeing sex as a taboo, and therefore bad, thing is not good for anyone. We need to teach children about it so that when they inevitably start having sex, they do it responsibly. They should be taught about LGBT content as well, so that they can be understanding and respectful of everyone.
Science has discovered that people are genetically disposed to homosexuality. A kid, just going through puberty, may find themselves extremely confused and maybe even concerned about thoughts or feeling they are experiencing. If LGBT content is taught in school, this might ease some of the stress that puberty places on them.
LGBT is actually a very small group. Despite what some sources say, I think about 6% at the most are LGBT. So there really is no need to teach sex involving a very small minority because most of the kids in a class probably just want to know how people get pregnant and the more important stuff. It is also my understanding that in higher levels of sex ed, non-vaginal sex is taught, so there's some help there. Kids also have the Internet nowadays if they get really desperate.
There should be an honest discussion about LGBT content in the child's home setting but not a teaching lesson in schools. There are many topics that are based discussed in the home setting and parents need to set an open and accepting attitude toward LGBT as a model to their children.
I think we talk enough about sexuality in the schools as it is. Refraining from adding another element will be okay. I remember at that age I would have been overwhelmed. I was dealing with enough with my own sexuality and noticing boys, the last thing I wanted to deal with was someone else's homosexuality. I think just explaining that we should not discriminate against others is the way to go and leave it at that.