jonathan18:
Yep, generally agree that you're on a hiding for nothing trying to build an impenetrable wall around one's kids.
First, whatever or however you as parents manage their access to content etc, it's virtually impossible trying the same degree of control outside of the home (school, friends etc);
Second, I'm not sure how well that approach works in building a child's ability to self-manage and respond appropriately. At least educating your kids in relation to dodgy content etc in your own space can help provide them with the tools to better respond when they do encounter it outside of the home. (Or they'll be less likely to go looking as it's not given the verboten allure).
Third, the tools provided by many tech companies to help 'protect' kids are, too often, complete sh!te. Here's looking at YouTube Kids, PS4 parental controls, Google FamilyLink...
It's a tough one because YouTube can bring so much content unavailable anywhere else. For example a child saving to buy a bike could use Youtube to watch reviews on various bike brands. Maybe one approach would be to make family restrictions based on age plus a lot of education about the internet. Maybe very young children only allowed to use the internet in family areas lounge kitchen an so on. Older ones gradually given more freedom. After all we expect 10 and 11 year olds to be mature enough to do road patrol at their schools.