Wattpad isn't built for kids, you have to be at least 13 just to make an account, if someone started reading something they didn't want to that person has the choice to stop reading. Personally I don't think it's right to stop people from reading what they want to, but i don't know i was on Wattpad when i was like 11 so i barely notice when something is 18+ content.
Ah maybe that's part of why they're doing that, because they don't think that you should be looking at it when you're that young because it exposes them to things that you're too young for