Sneaking ice cream out the freezer.

It was in one of those transparent tubs, and they would eat it from one side and put it back so that the side which was still full would face me and I couldn't tell they had eaten it (not being a fan of ice cream I rarely opened it).

When finally I decided to get the ice cream out for their pudding one day, I took out two tubs, both of which had the thinnest slither on one end on the tub creating the illusion that they were full.