Bringing a four-year-old on a flight with you will require some planning in advance. At the tender age of four, most kids just cannot sit still for the duration of a plane ride . At that age, children want to run around and play until they drop. Sitting still and being quiet aren't usually in a kid's skill set at that age. That's why many parents find themselves stocking up on snacks and charging up their iPad before they head to the airport. At least a lot of planes nowadays offer personal TV…