Good lord, what kind of a nasty person are you?
A two year old doesn't get pranked, FFS. This is a small child who can't shrug things off like you or I would. It would essentially simulate diaper rash. Might as well give the kid colic while you're at it.
I also don't believe for one minute that the parents (if they are at all competent) are agreeing to what, to a child, is cruelty.
If I knew any of you IRL I would be contacting CPS.
This is stupid, nasty, and anything but funny.