I don’t think you know many (or any) transgender people, adults or kids.  I know what I am talking about.  I know lots of trans people, several trans kids and am trans myself.

Nobody does this on a whim.  And no parent decides to change their kid's gender.  Most parents are anguished at first when their kid insists he or she is trans.  Kids who display serious, consistent gender dysphoria need to delay puberty until they can sort out their feelings.  Remember that puberty-blocking drugs are reversible.  Stop taking them and normal puberty resumes if you decide not to transition.

I hugely regret that I had to go through puberty before transitioning.  It made it much more difficult, though I am still immensely happy with how my life has turned out.