My two oldest grandsons, Bubby and Mac, love Scooby Doo and the idea of solving mysteries. So when I visited them in January, I brought along an old magnifying glass we had lying around.

The boys got a kick out of taking a closer look at bugs and rocks—as they previously had with a toy magnifying glass I once brought—and pretending they were on the path to discovering clues that might solve a case of an imaginary Scooby Doo and the gang sort.

When I packed my grandma bag for this current visit, I figured I'd...