You're unfortunately about to get the first lesson in running your daycare like a business. If you don't you will get absolutely ran over by your clients. You'll have very little chance in small claims court without a written contract. Cut ties with problem parent. For starters from now on-
1) written contract with parents. Be specific. There are several threads on contracts you can search for up top.
2) always get payment in advance. If they don't pay don't provide care.
3) payment is for enrollment not attendance. If you do part time (I don't) payment is due for the days agreed to.
Good luck with this.
We've all been there.