one word- clippers!
i shaved my son's head (not really short- a #2 for those of you familiar with clippers). my wife knew i was going to do it, but was still a bit shocked. others love it!
i think he looks really cute- takes 5 minutes and pays for itself in 2-3 cuts.
obviously, this is only for you if you want a child with really short hair. great for the summer though!