That's absolutely true, and that's why it's pointless to try to track everything they do. It gives the kid attacker's advantage - You have to stop them from getting through in a thousand ways, they only have to catch you not defending the castle once.

Which leads us to the question of goals. Why is it that this is a war? We already know we're going to lose, so all we achieve is blundering mutual trust.

Is the goal to slow them down from getting to see what they will manage to see anyway? Because by banning it, they'll be very interested in why it's banned, and you may well get it seen even earlier by providing that incentive.

I think the goal should be raising the child to be a well-adjusted, successful adult. Unless things go very wrong, they'll spend most of their lives as adults anyway.

And to that end, I'd argue a foundation of mutual trust, based on a parent and child being willing to approach each other and trust each other with their problems, even the ones that are embarrassing or difficult to talk about.

And therefore, I'd rather teach them how to be responsible and help them learn how to navigate an internet-connected life, than to try to box them up and present myself as an obstacle to get around. Because I believe that will provide a better foundation for a parent-child relationship, and for the development of a child into a person who will outlast me.