Dont want to get caught in the crossfire here, but altho it has to be 25 years ago, a little boy, I think he was 7 was taken from the streets of NY. His name was/is Etan Patz. he has never been found. That scared the living day lights out of me. I still think about that child and say a prayer now and again for his parents. That child was alone walking to school. Nothing at all wrong with keeping your young children under your wing. Nothing at all wrong with being aware of children alone and keeping a watchful eye on them.
In the case of the two year old described by the OP the mom was guilty of felony child endangerment. Had the authorities gotten there before the child was returned mom would have been arrested and charged. Too bad it did not go down that way as "mom" evidently did not learn a thing and the incident has probably been repeated many times by now. If I ever see a small child left unattended I will not hesitate to contact the authorities.
As we speak the City of Tucson is being turned upside down in what has been a vain search for a beautiful 6 year old little girl who apparently was abducted out of her bed while at home. Just that much easier for a sicko to snatch a child left unattended in a campground.