I agree with Emily, do it now. Revise your contract to include everything you want in there and then tell the parents that a new contract is being sent home for them to read, sign and return. Tell them that in order to run a successful day home and to lat out clear expectations of both yourself and the parents this contract needs to be followed...and then YOU need to enforce it! If you're not going to enforce your contract, they won't take you or your contract seriously. In your contract, you need to do set rates. They're paying for a spot, not the time they spend there and you need to start charging for stats (this would come with charging a set rate). Your time and service is valuable, you need to be paid for it!