He literally just told you the solution. Install uBlock Origin on your teens' phone and use the right filter list. Unless of course, they are smart enough.

Is it possible to install uBlock Origin on a mobile phone? I don't think it is. https://ublockorigin.com/

uBlock Origin can be used on Android phones through the Firefox browser, for example.

Very cool, didn't know firefox mobile supported extensions. Thanks!

... to change the browser extension settings, disable the extension, or use another browser, not to mention that uBlock isn't available on iOS

Yup. But apparently it seems like it might work for him. I do not know. They are probably smart enough to disable the extension. There are many other, fool-proof ways though.

If anyone has the patience and knowledge, you may chime in. :)

I remember I read a lot of these methods before here on HN. Some were pretty cool, and somewhat old-school yet effective.