Thanks everyone for your replies. Really appreciate your thoughts. I've got a bunch of small, clear, screw-top containers lying around so people's fingers would be perfectly safe when digging around in a cache. My concern was exactly kunarion's comment ("our 3-year-old found..." [and the story gets real exciting from here])…
I have a 3 year-old and he is just beginning to enjoy "treasure hunting." Personally I would never let him pull things out of a cache without checking first, but I don't want to be the cause of someone's little one getting hurt. It feels safe enough to me, but wanted to hear other's opinions.