My main concern here would be you have started off in a position where your clients are in control. This sets the tone for the rest of their time with you.

As uncomfortable as it will be you need to take charge. Otherwise any time something comes up and they don't have the money they will just not pay you until it is convenient for them.

If your policy is they pay BEFORE the weeks of care then their children do not step foot in the daycare until fees are paid.

Send a written letter at DROP OFF tomorrow morning noting fees are to be in hand at pick up. Let them know in writing that their not paying in full Friday will be considered their decision to terminate care immediately. You will quite possibly be out a weeks pay...but it will save you many potential future headaches.

The only way they should have been in care this week was if the parents discussed this with you at the signing of the contract. I get it, it can be really hard for some to come up with that initial payment. BUT their not bringing this to light and discussing it is a sign they feel they don't need to and that they believe they are in control. And frankly they are in control because they are receiving free care.