First a note: With any offsite projects be sure to get signed permission slips for each child.
Something that seems to help children develop a better perspective on life is to expose them to others in less than desirable circumstances. Combine that idea with a service/outreach project to plan a trip to a local nursing home or rescue mission during the holiday season. Plan a program in which either the children can sing Christmas carols or they can lead those visited in doing so. Be sure to plan a devotional and testimonies from the children in which the Gospel is clearly presented. Plays or puppet skits also go over well.
Most places appreciate visits at times other than during the Christmas season, but that might be an ideal time to plan your initial visit since many children (and parents) are more willing and inspired by the season to do things like this.