Any prank with starts with the general premise, "Lets drop **** on people from an airplane" is stupid. Add to that the timing of the prank, and it was the actions of morons.
Nope, adds to the funny. They would not be, I would though. That video of the kid getting hit with a basketball and falling down is pretty dang funny.
Getting hit by a water ballon going 300+ mph would be a little more painful. It might as well be a rock. That would not be funny.
The little kid getting hit with a basketball is a classic. Ouch! That has gotta hurt especially if you're a little kid. What are the odds of something like that happening?