I went to sleep when I was supposed to be watching the children
Why did you go to sleep when you were supposed to be watching them?
I was tired and I didn't want to watch the children any more.
It's very irresponsible to fall asleep when you're supposed to watch the children. It's dangerous to leave young children alone as they could be seriously injured by your negligence.
Kids need freedom and you should let them explore their wild side.
It's true kids need freedom but that doesn't mean they can be their own. They are curious about things and cannot see the danger at that age so as an adult it was your responsibility to keep an eye on them. If you're too tired either you should control your sleep or do not take the responsibility at all.