Sorry to hear that. That must be stressful for you.
I am not sure what your legal repercussions are or whether it will be worth your time and moneyto take them to small claims court. I am not familiar with what the costs might be or whether you have a good chance of recovering any money.
I think you might just have to take it as a loss and learn from it going forward...but that is just my opinion.
I would make sure you receive a SIGNED contract back at least two days or a week before any child starts in care and tell parents during the interview that it is mandatory to have the contract back X amount of days prior.
I would also ask either 1) a deposit before the ever starts or 2) payment for the week/days ahead on the first day of the week. I hold a deposit of one week's pay for all my parents. I know some other daycare providers in my area ask for payment upfront every Monday morning for the week ahead or else no care.
Either choice you are covered if they walk.
Worst thing that could happen to me is someone walks at the end of the week but at least I have a one week fee held that I would just use to cover my work for that week.
I hope you can get the matter straightened out. Maybe they will have the decency to pay you.
Maybe you could place a phonecall to them and ask them for the fees or ask them when they will pay you and remind them that you have given your time, provided food and care for those days and are fairly owed renumeration for those days and the work you put in.