Imagine you had a son or a daughter who's not at full age and who is in psychological treatment. S/he wants to quit therapy, but the psychologist advises against this and the law states that you as a parent have to decide. Do you let your son or daughter quit therapy?
No, I wouldn't.
29(40.3%)
Depends/something else (please leave a comment).
31(43.1%)
And yes, this is coming from someone who has been in this situation. I'm not going to discuss it in this forum, but I just wanted to state that for the record.
Also, the way you phrased it makes it sound like it's probably not a situation where the patient is a danger to himself/others. If s/he isn't, I give a tentative yes, my child can quit therapy.
That being said, I'd try to get to the bottom of WHY the child wants to quit. If it's something like an issue with the therapist, as someone else suggested, that's something I'd want to know about so I can look for a different therapist.