Madeleine was left in a hotel room very close to where her parents were eating at the time of the abduction. In fact she was checked on 3 times before the abduction. Mrs. McCann described the area as being so close that it was similar to eating in one's garden.
I'm going to try and find the article regarding the above in today's Times on the website - I'll post a link in my next post.
Now, that's not exactly 'not letting the kid out of your sight', but it's hardly the least safe of options, and would one really, reasonably, expect that there was a possibility of abduction in such circumstances? If you went to eat with some friends, and said friends had this arrangement for their child, would you seriously leap from your seat, vault over the table and charge to the child's room, to prevent pending abduction at any moment? I didn't think so.
I think blame for this sordid affair (not that leaping on our high horses and pointing the finger is helping anyone at all) ought to lie solely with the kidnapper.