I blogged about Mardi Gras masks three years ago on Filth Wizardry. They are a great way to let the kids go beserk with the glue. The ones we made back when the kids were really little were with old airline sleep masks and white glue. If you do decide to make some and you happen to have extra cardboard and some Dollar Store crepe paper streamers handy then these dresses would really complete the Carnival look :)
If you're more of the Pancake Day type than the Mardi Gras type then here's a link to the first ever post I wrote on Filth Wizardry back in 2008, showing the pancake art the kids love so much. Now that they are older and we have mustard bottles, they are capable of making their own squiggly pancake drawings.
Crafts from the archives here that might be useful to you for St Patrick's Day are these...
Last link is to Paul's latest contraption. He made the girls a hanging rail to go above their dressing up box, out of some PVC pipe over the weekend. It's made their bedroom look a lot less like an explosion in Goodwill ;)