Is there any way to put a password lock on a specific app?

is there any way to put a password lock on a specific app on my iPhone and iPads? My niece loves to sneak behind my back and watch bad content on YouTube and I need it to stop. I would like to find out if there is any way to prohibit her from opening the app with a password. I don not want to put any parental locks, screen limits, etc. on my devises because there are apps she is free to use on my devices. I just need her to stop using YouTube while not restricting myself.