Appropriate age group(s):
Preschool and Younger
Elementary School
Middle School
High School & Beyond

Estimated time to make this gift:
15 min. or less, each.

Materials:
Primary: 3" round ceramic disks

magnetic strips (or discs) w/lots of holding power! Don't scrimp on length of the strip, consider using 2 strips.

Greeting cards

White glue

Clear acrylic spray finish

OR paint it, like the ceramic wreath wall tile mentioned on someone else's post.

Instructions:
Affix the magnet strip(s) or disk to the backside of the tile. Use glue if needed.

Use a clear plastic lid (like a whipped topping lid) to make a template slighly smaller than the ceramic tile. Center it on a greeting card design, draw around it with a pencil, cut out the circle. Glue it to the front of the ceramic disc. Allow a little drying time.

At this point, the project is finished, in the child's view.
The parent can spray a light, protective coat of finish on later, or supervise this application by older children.

When dry, wrap in colorful tissue paper with curly ribbons.

Other comments or suggestions to consider:
If the magnet power is not sufficient, your pretty magnet will make a swan dive off the fridge. We got one as a gift, and it did dive! It only got one crack in the middle, which could not be seen in the front, so I squirted glue in there and it carried on for another 2 years of kitchen work.

Your cards can have holiday themes, or just be pretty or cute. Ours had a cat on it.

*Locating the ceramic discs was the tough part of this project! None to be found at our local hardware super-duper warehouse places. Ultimately, I found them almost by accident (a year after going on a quest for them) at a very large craft shop called Michael's Craft Store.
Even then, I could only buy the handful that was there at the time. Call Ahead! Save your sanity.