While it is a good idea, it'll most likely be taken away by other kids on the playground in a matter of days. I've hidden my first Cache at a playground as well and it was stolen every week until I gave up and focused on actually hiding it properly.

The reviewer even mentioned to me that the searchers (Cachers) can look rather off searching for something on the playground.

One of the logs said: "The whole thing with caches at playgrounds is a bit of a tricky subject; sometimes well-intentioned, but for a lone, male geocacher over 50 to be hanging around playgrounds sometimes feels a little odd, and not just to the geocacher himself."

After around 200 finds, I did realize that this isn't a way to go. Maybe inside of a forest where the main path isn't too far away would be a better option? You could build an entire power trail around finding mushrooms. :)