I once tried explaining to a young niece that the calories listed on a nutrition label are not the same as the standard calorie (defined as the energy required to raise the temperature of a gram of H2O by 1 degC) but are actually kilocalories, or 1000 times more than the standard. She thought I said "killer" calories and was afraid to eat her lunch! Her Mom suggested that the next time I mansplain to a child, I use the terms "big" and "little" calories, instead.