It is a natural thing. One side is usually larger than the other. Have you ever noticed how shoes fit. Usually one side is more comfortable than the other. Ignore the kids or tell them to look at themselves and find there larger side..Just smile if they don't connect. It's no big deal Don't sweat the small stuff:)
Are you right handed? You use it more then! Everyone's hands and feet are different sized per the side of the body they are on. They even tell you that if you are lost in the desert to pick a point on the horizon instead of just trying to walk straight, the deviation in foot size would make you walk in a large circle! lol I also used to date a girl that was a softball pitcher, her right arm was larger for obvious reasons.