I charge a monthly rate... when my day home kids go on holidays or to visit other parents somewhere else, they pay full rate to hold the spot. My one kid is gone for 2 weeks to his dads and I still expect and get a full month. I also charge for sick days whether theirs or mine... as long as I get paid, they can be wherever they want... home, work, doctors, etc... Also I get 2 weeks paid vacation through out the year. Just tell them that if they would like to keep the spot then you expect FULL payment.
I am in Alberta and I charge $400/month for after school care and $500/month for before and after. Hope this helps!
Also learned by mistake... always have a contract and make sure that EVERYTHING is in there. I forgot to put in that I ask for 30 days notice to end care and got screwed. Whether the kid will be there or not, you should be getting paid. If we only charged when the child was here then we would stand to lose a lot of income if a family member were to visit or whatever. You can always find a parent that is willing to follow your rules...