Sadly, I've witnessed this sort of negligence in real life; there was one occasion, in my city's downtown bus station, when a toddler of 18 months or wandered up to me and decided that I was his bestest buddy ever; none of the adults in the immediate vicinity had the air even of being associated with the kid.

I finally hoisted him up in the air and announced, "Does anybody belong to this?" Mom, who turned out to be all the way over at the opposite end of the station, glanced up from her cell phone conversation and hurried over to claim her son. Bonus points: she'd been alternating attention between the party on the line and a surrounding crowd of girlfriends--none of whom could evidently be bothered to keep an eye on the kid either. I could've walked off with him before anyone noticed!