Discussion about sexuality is fine in an age appropriate way, as is talking about sex. Neither of those things will encourage children to believe the impossible.
*People have sex, for pleasure and for reproduction.
*People have sexualities, which may be gay, straight, bi or asexual. A discussion of those things, therefore, is preparing children for later life, and teaching them that wherever they fit into it all is fine.
*Unless they have a DSD, however, people are born into one of two sexes, and cannot change from one to the other. There is no such thing as the wrong body, and telling children that there is, and that they can choose which sex they want to be is cruel, as they can’t.
I don’t mean to be picky, but lumping sex, sexuality and gender is, IMO, one of the things that have allowed TRAs to push their agenda. The constant cries of ’this is like the homophobia of the 80s’, or the suggestion that keeping men out of women’s spaces is akin to keeping people of colour out of ‘white spaces’ are very offensive.