Advent Calendars traditionally alter the order of the numbers to make them more of a puzzle so this gives the children an additional task. It might be worth discussing the muddled up numbers on the trucks of the train with the children. The children could use the printed page version to cut up the picture and re-arrange the trucks.
The linked tasks offer a new group activity for every day in the run up to Christmas. You could use the series of tasks as an opportunity to develop your class' skills in working as a group and get them to present their discoveries to their classmates.