Some cultures leave shoes out so that St. Nicholas can fill them with treats.
This could be done outside the classroom door during class for a wonderful surprise. This could be done on the exact day of St. Nicholas’s commemoration, the eve of December 6th.
Consider holding a festival for children close to this feast day, when the children could leave shoes out at the beginning of the session on a Saturday morning. During the festival, the children could make banners of St. Nicholas to be used for the Festal Liturgy in a procession of children before the Little Entrance.
If the bishop is coming for a visit soon, the children could learn to sing the greeting hymn for the bishop (see Orthodox Hymns for Children, Vol. 1, pg. 29).