As far as I know there is no specific letter for daycare. You have to compose your own. I'm currently working on one for my DD's daycare. It reads like this:
To Whom It May Concern:
DD will not be getting the varicella vaccine because it is against our religious beliefs.
Of course, I'll include actual names in the real letter
As far as public schools go, they should have a waiver or form for you to sign. Contact the school nurse, she should be able to help you.