Per Quran, you have to overtaken by intoxication of Iblis magic to next level of evil to be homosexual/bisexual, so I would make them aware of that, and my view, and try to reform them, but I wouldn't embrace their choice.
This is a choice to "rebel" and "play" early in childhood, and so I would also warn my child about the propaganda of the west and explain them about magic and demons and to guard against intrusion from Iblis.
I don't think it's possible to disown your child, he/she always is your child whether you like it or not.