Presumably they would be a bit older than pre-school, though.
I remember when I was about 8, I would regularly take a penny bus ride ( about 4 mile) over to Walney Island with a few friends and swim in the Irish Sea, not an adult in sight, let alone attendance. Mind you, this was back in the 50's.
Don't think it would happen these days.
I did leave them unattended for brief periods when they were babies, asleep in bed.
And then I went to Singapore where my four year old son often bogged off down to the Kampong alone. But the Chinese would never have allowed any harm to come to any child. And I had zilch control over him anyway. Brave little horror story he was.
Back in UK they were just used to going off on their own.
Happy memories for some of us, it seems. I once fell off a rope swing over The River Brent, and not an adult in sight. And I pulled my baby brother out of The Feeder before he drowned. It was life as we knew it.
Sadly, it isn't like that now. The disappearance of Madeleine changed all that.