I stayed up reading and I had my bedroom window open so I could hear them. Whenever the wind would start blowing really hard I would call out the window to them and ask them if they were sure they wanted to sleep outside. Every time I would hear, "Yes", so I finally gave up asking.
I had the hardest time falling asleep because I couldn't take a peek at them before I went to sleep. Every night before I go to bed I have to go and look at each of them to see if they are asleep. I then rearrange blankets, make sure they don't have too many books or toys in their beds, usually rearrange Aria (she is a little sleeping tornado and often has her feet sticking out of her crib) and give them all a little kiss goodnight. Hunter won't actually let me kiss him anymore, so I have to sneak it in when he's sleeping. Not being able to do that last night made for a hard time falling asleep. 
But of course all my worrying was for nothing, they survived and had a great time. Mike made them pancakes for breakfast and they are all out there now running and diving into the tent. Of course they want to sleep out there again tonight.