tile coasters

First...

Visualize really pretty images vs. Peanuts comics...

Like this one:

...and this one- both found at  Graphics Fairy.

(click SEARCH tab, then click "religious" or "flowers")

Jesswilde on Instructables shares the instructions for easy-peasy tile coasters.

Only supplies needed:

• 16 cent tiles
•  Mod Podge (or 3 parts white glue, 1 part water, add  2 Tbsp varnish for shine)
• pretty printouts of your saint or flower.  (I recommend laser prints or color copies, as inkjet tends to smear if overworked...)

Also, Jesswilde recommends sticky felt on the back to protect surfaces- I would do that step first with the girls, then the decoupage.

*Update- I've seen several pretty coaster tutorials online- theirs are more time-intensive, yet more durable. I understand that unless you seal these with a polyurethane spray, that the Mod Podge is not entirely waterproof.  Also, heat can damage the surface. Eep.
Soooo.... see Prudent Baby for a more durable, yet time-consuming, probably-not-one-meeting craft.  Otherwise, be sure to offer the disclaimer for the above coasters:
light use, no hot beverages.