Friends taking advantage of you

I have several friends who always seem to expect me to babysit their kids if their babysitter cancels or their daycare is closed. I wouldn’t mind if they didn’t expect me to feed them multiple meals and not give me any money for their food. I don’t expect them to pay me but I’d never expect someone else to feed and watch my child for free. If I say no they try to make me feel bad because I’m home already anyway so what’s watching one more kid 🤨. I’m currently contemplating going back to work just so people don’t assume I have a bunch of free time and to get some adult interaction again. Is it unreasonable not to expect people to think you are a free babysitter?