Crazy Cranky Kids

Why have my kids been so cranky today? I thought at first maybe it's just Monday crankiness, but today is a holiday. There is no school, no work and we have just been doing chores and the kids have been playing. We even slept in this morning. Is there a full moon? I mean, my kids are beyond cranky - they are out of control, crazy, grumpy, rude, not listening, hitting each other, and the list goes on. Is anybody else's day like this? It's making me cranky just writing about it.