We all know human's can't change sex. If OPs son actually think's they are a woman then that is a mental disorder.
I'm not true that's true anymore @lifeturnsonadime.
For the past few years 'we' have been educating youngsters on the importance of gender and that you literally are the gender you identify as, which may or may not match your sexed body.
I think it's all nonsense of course, but I'm an oldie unlike OP's DC.