Formally it is perfectly correct as "себя" refers to the subject of the sentence. But I agree that for the ear of native speaker it can be a bit ambiguous. For the better style I propose to remove reflexive pronoun at all:
Он заставил своего ребёнка целый час ждать возле школы.
Even better:
Он заставил ребёнка целый час ждать возле школы.
Well... if someone needs a literary master-class in Russian...![]()