Advice desperately needed

I have developed a friendly relationship with two parents and they have agreed to pay me three days/ week regardless if the child is there or not. Now I've somehow become a drop in center and don't know how to fix this. I've been too lenient but now that my daycare is on a roll I don't how to change things. I'm getting texts asking if I could watch their kids a few hours here and there a day before I'm needed although I've asked for schedule a week in advance. Why do I feel guilty saying I can't accomadate them!? How do I change this?

You need to sit them down and get them to sign a contract with set schedule on it. IF they don't want to do that, then let them know clearly you may not be able to accommodate them and will continue to be interviewing. You have to stand up for your business