If children think that they are the wrong gender they are lovingly but firmly told that it doesn't work like that. It is not possible to change biology and to use it as an opportunity to explore what the underlying issues are, whether that be jumping on a bandwagon or legitimate feelings of gender dysphoria.They know it, they just don't care as their needs take precedence. Society needs to get a grip and stop treating children like emperors.
However, I think that this agenda has been initiated and led by adults. Even the CEO of the charity Mermaids makes it sound as if she were solely responding to her child's desire to change gender. If you hear the whole story she explicitly states that her husband didn't want a gay son.
The most vociferous voices in all of this seems to be adult men.
Edited to remove divvy cut & paste error