I would like to see photos or a plan of the area and how the little one managed to get through so easily, without being noticed.
We all know as parents and grand-parents how quickly things can happen with toddlers- however we normally make sure we anticipate trouble. There are places where you just don't let go- ever, never.
Talking about negligence and prosecuting parents- not sure it would help, really? Last year here we had a tragedy I still can't understand. A father from nearby France, working over the border, was supposed to drop the 1 year old baby at the nursery on his way. The child fell asleep in his seat- and as he was stressed due to work deadlines, he forgot all about the baby- who was left in the car in the car park all day- and died. The father was incredibly not prosecuted- as it was said he had suffered enough. I can understand, perhaps, forgetting about the child for a few minutes or 1 hour or so- but surely at some point you'd jump and think 'OMG - I've forgotten little one' - but apparently he totally forgot till the evening. Did no-one hear or see the child??? Did they walk away thinking it was none of their business and shouldn't get involved- I still can't get over it (and wouldn't like to have to live with theri conscience) (: so tragic.