Kevin was 3 and Katie was 1. They had just gotten a train for Christmas (with financial assistance from their Grandmother, Memaw). There were two rider cars, the engine and the passenger car. They had a couple other cars (flat car and caboose) that are not attached in this picture.
Anyway, Kevin thought that the Engineer was the best spot because he ran the train.
But Katie knew that the Conductor is the one who is really in charge. So it worked out fine.
Source: Bob Cook