blinky-
I would never be sarcastic with an issue as serious as this.
The mother was definitely wrong for leaving her kids out alone, I wanted to bring up the issue of securing a play area which people, like myself, who do not go to the country, are not used to doing.
At the end I mentioned again not to leave children unattended as it can never be said enough times.
But you are correct, it is first and foremost the responsibility of the parents to make sure their children are being properly supervised at all times.