If Ron, Josh and Cory were my kid's uncles, and they offered to take my kid to the parks, this is how I picture it playing out:
Ron: Kid comes back a little sunburned, soaking wet, missing a shoe, and sick from eating too much junk food, but says he had the best day ever. There's also a vague story about almost falling off of, under or into something, but Uncle Ron says don't worry about that - it was nothing.
Josh: Kid comes back exactly the same as when he left, but crying because he didn't get to ride anything fun, or go in the play areas, or even get out of the stroller. He's also starving, because Uncle Josh didn't buy him any snacks; supposedly because he wasn't sure about kid's dietary restrictions and food allergies, but really it's because he's cheap.
Cory: Trick question - everyone in the family knows you don't leave any of the nieces or nephews alone with Uncle Cory, no matter how many times he offers.