The thoughts on this vary greatly by caregiver and by location.

Ultimately it is your business and you are free to do as you please...BUT you do need to have it in writing and to have all parents aware of it before they sign the contract. If they do not like it they are not the right family for YOUR business.

If you have already been charging but haven't formally had it in writing then I would say add it to an updated contract. Send it out to be read and signed. This would be a time to add anything else that you feel is needed or to clarify wording on sections you feel have been misunderstood.