Here's a nice and inexpensive "scratch off" Advent Calendar
that reveals "the gifts we've been given in Christ"

You can get it from WeAreKidMin -- the artistic resource ministry of Dema Kohen (lot of interesting Sunday School teaching/art materials on their site). I purchased one to give it a close look and it's a really nice shiny 18x24" poster with 25 big scratch-off circles -- the kind of thing kids enjoy and should prompt discussion.

From the site: "Helps busy parents make sacred pauses in the beginning of each day to help them together with their children discover all the wonderful gifts we’ve been given in Christ."

This photo of the heavy stock poster from their website shows the "scratch off" circles scratched off.

The version I received also had a blue background, though it looks white in my photo. It came rolled in a postertube. And of course, as you can see in my photo below, the "scratch off" circles are silver when you get the poster. I paid $6 for it.

In addition to home use, you could use it in your classroom -- scratching off several of the "blessings/gifts" each Sunday and discussing them, or it can be given to families with children of a certain age. (Ages 5 through 9 feels like its sweet spot since the subject is "blessings" and not candy like you find in other Advent calendars).

I can also see how this particular Advent Calendar could be a template for a much larger display that could be made for the congregation, or individual calendars made by kids for home use inspired by the WeAreKidMin scratch off calendar.

BTW: You can make your own "scratch off" stickers for your own Advent Calendar by "painting" pieces of clear contact paper that you've precut into circles or squares or shapes. After the scratch off paint has dried, you stick the painted clear sticker --sticky side down over the thing you want to reveal. This craft blog has a simple recipe for making "scratch off paint" using acrylic paint and a bit of dish soap. Simple.