I would hand it in to the police, no thought required.
Over the years I have handed in a few things that I have found, a gold watch and more recently when my daughter was in her very early teens she found a gold bracelet. After the specified period of time we checked with the police station and as the items were not claimed they became our property and we could wear them with a clear conscience.
Someone handed in my credit card folder when I dropped it, I was very grateful - 'do as you would be done by'. Honesty pays.
When I have found a very small sum of money, perhaps a pound or so then I put it in a charity box.
_________________________
Many a child has been spoiled because you can't spank a Grandma!