SquidSoap

Kids don't like washing their hands, and even when you can get them to do it, they probably don't do it very thoroughly. But when kids push down on the SquidSoap dispenser, a black an orange ink mark is made on their palm, and unless they scrub enough to remove it, you'll be able to tell they haven't washed well. It takes 15 to 20 seconds of washing to remove the mark, which, coincidentally, is the doctor-recommended hand-washing time. $15.99 USD for four.