"Not all children are at risk when they are left unwatched for a while. All parents do it. That's a normal part of life. "
It all depends on the circumstances. Of course you don't watch them every minute of the day, but in a public building (or even a hotel) you keep a closer eye on them than when they are in your own home - and you should certainly (at that age) have a baby monitor active if they are out of 'normal' ear-shot. what if she had woken and needed a parent?
Sorry, but the MacCanns were at fault, not just the person who kidnapped her. At the very least, they made it easy for him.