Son can speak? Or you or wife can speak?
My friend doter rejected, she and whole family can't speak/read, teacher said its little late at least must send to kindergarden with mandarin, and teacher advise to go fast track mandarin class, teacher said sked later will have problem, because who will help her at home where there is nobody can speak/read when she need something to refer.

But if die die insist want can, they will monitor the kid, if cannot go school will advise to go normal SK school.