The reason of not giving permission to the parents might be their care for their children.
We may grow bad if we do not listen to our parents and they are the ones who nurture us right from the beginning and do not want us to go on the wrong path. They love us a lot, but we take these love for granted and give them the name "Over-Security" or "Bound to do". We do not enjoy our self life. Also if a wrong friend is great with their son then he can also mislead him and take him away from his parents. The parent may also think that the child must have a grudge against their son so he might poison him, etc. Also the greatest care is from the parents towards their child. There are some slang, adult content, etc. included in those movies nowadays and the parents do not want their child to know thatand induldge himself in such malpractices.