It doesn't take much effort to find things the British establishment won't want kids seeing even though kids talk about them in school playgrounds (or at least we did when I was last in a school a bit over 23 years ago).
For example, I was given a summary of The Texas Chainsaw Massacre by some girl in the same class as me when I was 8 or 9.
And even as an adult, you really don't want to see a real photograph of a newborn with anencephaly, which Wikipedia did have when I was first looking up the condition.
The point of Wikipedia — that it can be edited at any time — absolutely makes it impossible to survive any age rating system other than "adults only".