A minor under the age of 18 can refuse medical treatment but only if that minor has been emancipated by the court which means that the minor is legally responsible for their own well being and makes their own decisions legally.
However if you're a minor and have not been emancipated then no you cannot refuse medical treatment should your parents make the decision to take you to the hospital or doctor for treatment.
If you were able to refuse medical treatment then your parents could be in trouble if you're not emancipated so it's very important for parents to seek medical treatment for minors especially young kids.