Why is it?

Why is it on the days we have obligations and must get up early, I have to shake my kids, drag them out of bed, and prop them in the corner to get them dressed?

BUT......

On the days where we have no obligations and they can sleep in as late as they want, they wake up at the same time as the other days? Not only that...but they are UP and playing and yelling and having a great time?

I was hoping for a sleep-in kind of day today. No such luck.