The old folks pranks reminded me of this:
Setting: My wife and (then 10yo) daughter in the parked car listening to a CD.
Me: Outside with my new hydraulic jack .. having placed it under the passenger side of the car where my daughter was sitting.
Pump. pump pump .. to make the car jerk upwards ..
Priceless: The surprised look on my daughter's face: Her eyes were as big as saucers! .. like what is happening???!!
My wife was only slightly amused!