When I was child, I had a little toy box that looked like a pirate's chest. There was serial on "The Mickey Mouse Club" (circa 1955) where the Hardy Boys (a pair of young detectives who were featured in a series of youth books. The series started in 1927 and was then revised and revived in 1959.) were looking for a treasure that was hidden in an old tower. During the introduction, a pair of withered, skinny hands, reached into a chest of gold coins, moved them around and scooped up a few. I used to fill my treasure chest with cents and pretend that I was re-enacting that scene. It worked better if there were brand new red cents in the chest, of course. If you were to find such a toy, it might be a collectors' item now. At any rate your nephews would have to find some way remember where they buried their treasure. Like real pirates, it would have to be so many paces from a given tree or perhaps a bit more involved than that. Otherwise others might their "booty."
Yeah, but after they wear themselves out with looking , and you go into the act of using a dousing rod and can't find it and all the kids start crying.........it will cost you a lot of Grandpa' points