I think I would let them continue as they have been since this was not part of the original agreement and you have not had issues with them. I am changing my hours slightly from 5:30 to 5pm pick-up, but only for new clients as I don't feel it's fair to current clients to change it as the hours were part of the reason they chose me. I also have parents paying at all different times depending on when they started and some are biweekly and some monthly, but all are in advance. This doesn't bother me as I always have money coming in. However, I can understand the parents being a bit taken aback at the sudden change since they have always paid. If it is their only experience with daycare, they probably don't know that most providers get paid in advance.