I have been to walmart two times this week both times, we went through the self check out and both times money was left behind. The first time only a dollar, the second time 20 dollars. The first time my son found it and he was so excited and I told him that it wasnt his money, so he took it to the lady upfront and gave it to her. (he is 5 by the way) the second time he found the money he took it up to the lady and told her and then the lady that forgot the money came in and she was so panicked looking for the money. I told her my son just took it up front. She got her money back and went up to my son and shaked his had and told him how greatful she was.
So the best thing I think we can do is teach our children to be honest and teach them to pay it foward.