I know how you feel. I was coming back from the restroom when I see this little girl climbing on the side of a bin of $5 movies. This bin is huge and made of metal, something that could hurt someone climbing on it. So I kindly asked her not to climb on it. Well, later I find out the mother (who was standing right there - yeah, nice parenting skills) had complained saying I was rude to her daughter. Uh, no. I was asking your daughter not to climb on something that could hurt her. Therefore I was looking after her safety.
People are just unbelievable.
And I've actually yelled at kids to stop running in the store. At first I ask nicely, then I just yell at them. I've had a couple parents see their kids running, hear me telling them to stop, and jump in to scold their kids. Then of course I get those one or two parents who yell at me for saying something to their kid.
ME: *sees kid running by large 80" TV* Stop running in the store
AP (asshole parent): *walks over* Did you just tell my kid what to do?
ME: I told your kid to stop running in an area where he could hurt himself. I've seen plenty of people get hurt because they're running and I rather not have that happen to your son
AP: Don't you fucking talk to my kid like that! EVER! He's not your responsibility.
ME: You are absolutely right. He's not. You know what is? Making sure this place remains a safe and stress free environment. So if that means telling someone not to run in my department, then I'm going to tell them that. I don't care who it is. It isn't just for my sake or for yours, it's for the sake of your son. Oh, and don't swear at me again. It's uncalled for. Have a nice day