One idea (Score 1)

Not feasible for most homeowners, but here's an idea:

Setup a server in a secure room in your house that is always locked, has no windows, etc. Give your child a dummy interface to that server that only allows them to do very very basic things, ie, surf the internet. Limit the sites they can view only to a very small subset of trusted sites, and block everything else.

I'm not sure how i would go about bypassing that configuration.