I would tell them how proud I am that I raised them to believe that they could tell me anything, and for accepting who they are and brave enough to show it to the world.
And let them know that I love them, and that will never change no matter what they do, or who they are, or who they love.
There is nothing “wrong” or “abnormal” about it, it’s who they are, it’s something you are born with, not a choice you make in the heat of the moment or wanna try out for “fun”. Some know when they’re young, some take longer time to figure things out, accept who they are, some spend their entire life in denial.
I think the absolute worst that could happen, is that my child wouldn’t be able to tell me, out of fear of being rejected and that it somehow would change the way I saw them. That’s when you’ve failed as a parent, when your own flesh and blood is terrified of being who they are, that you won’t be able to accept them.
I’m all for people being able to love who they want. The only thing wrong with being LGBTQ etc, is the ignorant people who spend their time suppressing, hating…. It’s not the gays who need to change, it’s the way the rest of the world see them.
In fact, I recall reading something about the ancient romans having male lovers. It’s not a new thing, the only thing that’s changed is that people have started to become more open about it.