IMO, and I KNOW it is not this simple but... have to say it, parents have a responsibility to teach their children what is harmful and what isn't. If you have a pool, teach your kids to swim, teach them to doggy paddle, teach them where the steps are, and teach them not to go in the water if there is no adult present. More importantly and something that IMO has gone by the wayside, teach them about the CONSEQUENCES. I recall learning not to put my hand into the garbage disposal. I remember learning what happens when things catch on fire.
Accidents absolutely happen - I do hope that's what this was but, well, we just have to wait and see. Regardless, terribly, terribly tragic.
I agree with you to a point, as I was the same as a child. Didn't need cupboard locks on the cupboard with the bleach because I had been taught to not touch things like that, and I listened.
But I also think some children have such overwhelming curiosity and take a lot longer than others to become aware of dangers and consequences.