seems to happen at all ages https://nypost.com/2021/01/28/school-security-guard-busted-for-alleged-sexual-abuse/
But the rules are different for "witnesses" where the kid only has to promise to not lie.
The difference is that children under 8 are nearly guaranteed to not understand.
with the really young, they send them to child psychologists who have dolls and ask them where the perp touched them. Then the doc testifies.
(post is archived)