So tell me exactly with statistics how many people have left their children:
All under 4; in an unlocked residence; with no protection; infrequent checks which are not independently verified; for several nights in a row; whilst out drinking and snacking with some associates ?
I await your reasoned answer backed up with data. 
I know I'm going to be persecuted by what I'm about to write, but I'm used to it.
First of all, from the limited experience that I have with British couples with young children, both in Britain and in Portugal, I've never witnessed any of them leaving 3 year old, or even until they were in their middle or late teens.
Second, even though it seems all of the 9 persons assumed to leaving their children alone, I have trouble believing it.
Third, and it's here that I will be flogged, because it's speculation, I think that whatever happened had little to do with the reported neglect, and that was used to justify the absence of the child.
If there was a fatal accident, and there was the need to occult the body, then there was some very serious crime committed that could be revealed by the poor child's corpse. As I said this is pure speculation on my part - I have no clue whatsoever.