My problem with the kids I'm currently babysitting?

Hello.
I just started babysitting those 2 boys aged 11 and 13. The problem is as soon as their mother left they jumped on me and took my shoes and socks and told me that as I’m their “slave” I have to stay barefoot entire time. I gotta say I found this really uncomfortable as I’m wouldn’t take my socks even at my home. And when their mother came back and saw me barefoot I told her about their “rule” and she just laughed and told me that it’s not a big deal and told me “get on with it”.
Am I really making this a big deal? I have to go there today again, what should be my response if they demand my socks again?
Updates
+1 y
To answer some of your questions together:
The kids won't take no for an answer. I can't quit the job because this job is actually a lame punishment given by my mom. So I don't know what to do.
My problem with the kids I'm currently babysitting?
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