I had a similar sleepless night recently Maggot, when my kids (8 & 4) decided they wanted to sleep in our VW Camper, on the drive. I thought it was a great idea too, but ended up spending all night in the kitchen, looking out of the window every 18 seconds or so to make sure they were ok.
When one of my boys was about ten years old he asked if he and two mates could camp in the back garden overnight. Before nightfall though one of the chums backed out after hearing about a murderer escaping from jail about two hundred miles away. His mum had mentioned that escaped murderers had to sleep somewhere and he could get into our garden? It ended up with only two campers.
As an 11-year-old I used to love sleeping out in the 'wild'.
I'd go to bed as normal, then when my folks went to bed, I'd sneak out and meet up with a couple of mates.
We'd make a fire and have a fry-up first, of course , then creep into our sleeping bags and tell stories to each other. One of us had an alarm clock and we'd make sure we got home before our families discovered that we were gone. I shared a room with my brother and he was sworn to secrecy. Otherwise he'd get a duffing.
We didn't go out if it was wet or too cold.
I think kids should be encouraged/forced to sleep in the open from time to time; 'tis character building.