is finding $50 bad?

So my girlfriend and I were in target today and we look down and see a $50 with a couple receipts. We pick it up and flee the scene to look at it. We went around and picked up some more things to buy and saw the apparent girl that lost it at the customer service desk cryin about it. She was about 14. Was it bad that we didn't turn it in? If it was personal stuff, ya, but it was just plain cash . What do ya all think?