The first image in this section shows it is a switch at the bottom of the Parental Controls settings: https://staticmedia.kagi.com/family/parental.png

I couldn't find that either. But did find myself laughing at the "always check this with an adult" disclaimer on the quick answers. It's nice to imagine an alternate world where being an adult is sufficient for proper critical thinking.

It show up when you put a "?" at the end of your query.