My Q, your A: someone else disciplining your child

Here's a new occasional feature: I'll bring up something that happened to me recently, and you tell me how you'd react to it.

A few days ago I was with the boys (4 and 1) at the playground. Also there were a couple of El C's (the 4-year-old's) friends with their moms or nannies. One nanny, S, always drops off and picks up at school, and she and the kids she cares for are often at the playground. So we've spent some time sitting together chatting while the kids play, and we're certainly friendly, although I wouldn't consider us actual friends. I think she's an excellent nanny, firm but loving, and she gives the kids enough freedom but is also on top of any potentially bad situations almost before they start happening.

At one point I was standing helping El P (the 1-year-old) cruise around a play structure and chatting to a friend at the same time. S walked over, holding onto El C's arm, and said, "He's not allowed into the sand anymore today. He just kicked sand in a little girl's face." And then she delivered El C to me and went back to supervise her kids. I asked El C what happened and he confirmed that he'd kicked sand ("because they wouldn't give me back my shovel, Mom!" I was hoping we'd be past this by now. Sigh.).

Edited to add: S's charge and El C both had to be at school in a little over an hour, so S and the kids and I all knew we had 45 minutes left at the playground, max.

Question #1: How would you feel about S coming over to tell you what happened?

#2: About removing your child from the situation?

#3: About telling him he couldn't go back into the sand that day?

Does it change or add anything if we factor in the facts that I'm a white US-born American (as are my kids) while S is an immigrant of color?

So think about your reaction. Here's mine:

I was happy she stopped El C and then stepped in swiftly and decisively to remove him from the sandbox and punish him by banning him for the rest of the day. I think it's convenient that that's exactly what I would have done, but even if it wasn't my first instinct I hope I'd have been OK with it.

I have in the past been very upset when someone else at the playground disciplined my child, but I think this was different because: 1) I know and respect S already--it wasn't just a stranger hopping in who I knew didn't know my child. 2) She wasn't at all hostile about it, to him or to me--I will never forget the time El C accidentally knocked over a smaller kid on the playground and the mother told him he was "a bad kid." Uh, no. 3) I knew the only reason I hadn't been there on top of it myself was because I was with the baby. I think often if we get upset about someone else disciplining our child it's because we actually feel defensive because we know we should have been there instead of talking to another parent or being otherwise distracted.

To me this episode felt like a validation of the idea that the community can help you raise your kids. But I'm wondering if you had the same reaction to hearing the story, if you would have felt differently, or if you have other insights into the situation. How do we negotiate others disciplining our kids (besides regular babysitters and others we assume will do it daily)?