One of my recent proud moments as a parent was catching my 7yo up at midnight reading her favourite book of Greek myths.* I can verify it's not actually possible to tell a child off for doing precisely what you both did as kids and deeply approve of. I actually convinced her she did need to sleep by pointing out how tired she'd been that morning, and she did have school in the morning ...

* http://www.amazon.com/Atticus-Storytellers-100-Greek-Myths/d... - simplified and bowdlerised versions for kids, but a really good start on cultural literacy.