I was just wondering about the with parental permission clause

I've seen many children posting who are younger than 15 , young as 7
( I mean nothing against the kids,some of them are pretty darn smart).

But I was just wondering, how could lichess possibly verify parental permission?

I guess it doesn't have to. Certainly, any children younger than 15 are supposed to be in kid mode, which means they can't post. So they, or their parent/coach have violated the TOS.