Should I mind my own business when I see or hear a parent disciplining a kid?

I work part time on the cleaning crew at my local mall. A couple of times each month, a parent will pull one of their little brats into the service corridor to scream at them or them. They don't realize that I'm just down the hall in the utility room washing mops or hanging up brooms. Today, some guy gave his son 10 whacks with a belt 'cause he tried to steal something. My partner says to mind my own business. What should I do?