After all, if you're traveling with children, you're likely unpacking and re-packing practically the entire contents of your three carry on bags in the span of a few minutes. Simultaneously unbuckling your pants, taking off your kids' shoes, and ensuring the kids' DVD players--so desperately required for the 12 hour flight--doesn't get confiscated because you neglected to put it in its own bin on the conveyor belt.
Ditto for the emergency boxes of aseptic milk you packed.