My 9 year old (but quite immature in life experience) DS has told us two things this week that he learnt at school.
The first is; it's manly to walk up to girls and thrust your hips at them in the style of Grease Summer Lovin'.
The second? It's unnatural/wrong (his words) to like your little brother or sister.
He told DH he'd learnt about sex but we think that's related to the thrusting...