Anytime you leave your kids unsupervised in a public place you are taking a risk. Most parents will assess that risk and decide whether it's low enough to be acceptable to whatever personal measure they have on the subject.
Also, it's pointless trying to compare crime numbers on an overall basis. Try comparing them on a per head basis and you'llhave something more valid.
I'm pretty sure that the OP was not blaming the parents for the crime rather suggesting that their actions were a contributing factor to the situation.