I check, but not for safety reasons, just to check duvet is on and to remove stash of books and the nightlight that are invariably stashed literally under DD in bed... She seems to think its comfy!
On a slightly separate note though, one DD is three and, before it was clearly very sinister, lots of comments on newspaper articles etc were saying "a three year old could never open the door" etc... Tbh, I'm pretty sure my three year old could if she really decided to. For instance, I was putting her younger siblings (just a few months old) down for a nap a few days ago, and in that ten mins she'd got pretty far into making an omelette....! Put apron on, got chair from dining room to stand on, got bowl, broken eggs, got frying pan.... Thankfully hadn't got as far as cooking! I'd left her watching Tinkerbell, for ten mins! So yes, if I hadn't double locked the front door (she'd lack the strength for a Chubb lock), I'm pretty sure she could get out in the night without me knowing while I slept.... Horrid thought!!
I also saw lots of nasty comments commenting on a 9pm bedtime. I nannied in my year abroad fit a v posh family in Italy. 9 or later definitely the norm for kids there as they have a long afternoon nap until, well, adulthood!!