I think it is pretty straight forward as well. You give a family 2 weeks off without payment so it is simple. They either pay you full rate or use this time as their 2 weeks unpaid holidays.

I don't have an expiration date in my contracts but it does state that I reserve the right to change my contract at any time and will provide 1 months notice of any major changes. I usually hand out new contracts every December with a start date of January 1st. There are always issues that pop up over the year that I feel need to be included.

Yes I also hope you are getting paid in advance!

I recently switched my contract and now offer my parents a discounted rate on time their child is away. I charge full rate for stats but if a family takes holidays I charge $5 less providing I get 1 months notice. No notice, no discount. It has helped a lot! I was finding that parents were not keeping their kids home or taking holidays because they had to pay me (oh the horror to have to pay while your child is away lol). This has given them an incentive to keep their children home more and to give me notice. I do not give any parents unpaid holiday time though. They are paying for the spot!