Can you believe that despite a childhood in BOSTON, of all places, I never understood an iota of what St. Patrick's Day was all about? I had a vague impression of leprechauns, shamrocks, and Irish jigging, and that was about it.
Then my kids and I learned about the real [St.] Patrick in our medieval history study a couple years ago. If you're interested, Adventures in Odyssey makes a gripping retelling of the story in the episode "Patrick: A Heart Afire" which can be downloaded from iTunes or bought as part of the album Days to Remember. Warning: This episode can be a bit intense, and alludes to the human sacrifices the early Celts made, so consider your child's age and sensitivity.