Does anyone know if it is possible to just block the Youtube app on mobile phones from connecting?

I have configured Netshield block website feature to block a few websites using guidance from https://superuser.com/questions/713289/blocking-youtube-android-app-from-router and have managed to totally block Youtube for desktops as well as the app.

Ideally I would like to find a way of just preventing the app from connecting, but still let the desktop site work. My son has an iPhone, and I cannot find a way of individually blocking the app on the phone short of deleting the app.