Oh you absolutely did the right thing! They would have found it at some point.
Last year we (me, hubby, 9 yr old son) were sitting in the window of a cafe at the Bellagio in Las Vegas. My son suddenly said "MOM, THAT LADY JUST DROPPED 5.00". So I asked him if he could see the lady. He said yes that she was in line. So I told him to go grab it and give it to her. He did, and she was so impressed with his honesty that she gave it to him. She even came over to us and congratulated us on such a "fabulous, honest young man". She was an older lady and she said " I hope you don't take offense to this. But it gives me faith in young parents again. It just seems that I see a lot of HORRIBLE parenting these days." Yep ma'am, there is a lot out there. But there are also just as many GOOD parents, so have faith...