I agree with the PPs -- pick the days YOU want off, and give the dates to each of your families, along with a note saying that they are responsible for paying for every other day, whether they're there or not. And then put it in your contract for next year
. I have one week off over Christmas each year, and I let the parents know in advance. It took a bit for some of them to get used to it, but now they know that whatever days I'm open, they pay for on their last day of care beforehand.