> what can I do to keep them away from stuff 99% of people agree isn't for children to see, without something like this?

The better question is "Why do I need to give up privacy on my devices that no children ever use and are used for all sorts of mundane things that are entirely unrelated to what you're trying to protect your children from to solve this problem?" The solution being proposed here is to require ID checks at the OS installation level; this would be like requiring me to flash my ID when I walk out of my house because kids would have to go outside if they were going to try to buy alcohol.