Maybe there are SOME people whose sexual expression is a result of being abused, but in general orientation is orientation. I'm bisexual/sexually fluid and in my experience, sexuality changes over the course of your life. Mine has a lot (although I've always been bisexual, my sexual expression has varied a lot). I suffered verbal/physical abuse but not sexual. I actually shelved the idea of being bisexual when I was twelve because I read about maternal transference in a psych textbook in our house and was like "Oh, I'm not bisexual then, it's because I have a bad mother." LOL. Kids shouldn't read Freud.
One thing, I never thought I was trans, but I have definitely always wanted to be 'gender-neutral' in the workplace (I'm a woman) and I wonder if the kids' rejection of gender identity is a broader rejection of patriarchy/sexism or an actual thing. Because certainly there are three biological sexes (male/female/intersex) and I wonder like, back in caveman days, if there were naturally occurring cavemen who were like "no I'm neither out nor in" (excuse my assumptions of cavepeoples' rudimentary language skills). I definitely grew up knowing the world believed boys were arbitrarily better than girls, and that my mother didn't want me, she wanted a boy, but I always outperformed the boys in school so it confused me.
I pretended to be a tomboy for my mom to like me and once I started working in my early 20s I used to say all the time I wish I could be gender-neutral at work. It's so weird, how men treat you. I went from always being the dumpy friend with the personality to the "cute young executive just in this meeting so [so and so] has something good to look at!" Wtf how did that reaction towards me change so fast?