The friend likely said this to the narrator as a playful tease or to challenge his belief in magic, perhaps thinking the narrator is too old to believe in Santa. The narrator is listening anyway because he still holds onto the wonder and hope of Christmas, wanting to believe in the magic despite what others say.
Yes, I think the other children on board were having similar thoughts — feelings of excitement, awe, and anticipation for Christmas Eve. The Polar Express likely has a specific purpose: to transport children who still believe in Santa Claus to the North Pole to witness the start of Christmas, reinforcing the power of belief and the spirit of the holiday.
Parent Tip: Review the logic above to help your child master the concept of polar express worksheet free.