Henry: I'm so tiiireeed.... DX
Me: Then sleep. 
Henry: Caaaaan't...
Me: Why not? 
Henry: Cuz there's so much stuff I gotta do in the morning...
Me: ...Well... that would be a pretty good reason to sleep now...
Henry: I gotta get up at six, dude.
Me: ...I know. That's why you should go to bed now. So you can sleep well enough before six tomorrow morning...
Henry: But what if I [i]can't[/i] sleep enough before then?
Me: ...You're overthinking sleep. I didn't think that was possible, but you've managed to pull it off. Just sleep.