Those Pesky Leprechauns

To hear my daughters tell it, St. Patrick's Day is going to be something straight out of a horror movie. I'm partially to blame. To get them ready, I told them all about how they'll be wearing green to school next Wednesday. Then I mentioned leprechauns. Oops.
My intention had been to use green food coloring in their milk next week. To prepare them, I told them leprechauns come and play tricks... nothing mean, just silly pranks. Big mistake.
First, they were terrified at the prospect of little "things" coming in their house. They're convinced that if the milk is green it will taste like broccoli. They are now discussing what treasured items they need to hide so the leprechauns won't steal them (blankies, toys, etc.).
So, I'm looking for suggestions. Green milk is out. What simple, fun thing can I do to show them leprechauns mean no harm?