how to prevent youtube sexy videos !! in my child iphone

hi ,

sorry my english is not so good but you will understand

i am mad ,,!!

my child is using his iphone " youtube app " to search for sexy videos!!

i didnt find a way to prevent that ... ! and i cant hide youtube form he becuse he needs it in his studies !!!

just find me a ways to prevent these kind of videos like teen lesbian , asian kiss

if you said its not sex !! i will !! he start searching for asian guys kiss !!

i need a programm that can prevent these videos but in the same time allow him to search for his studies or anything useful

and i alos post in youtube!

i need this now !