The parent should have been watching the child, PERIOD! It was just plain disrespectful -of the parent. You have to teach your children from the begining.
I have a toddler and like another post said, I'm on her like "white on rice" all the time. Not because she's bad, because she 2 1/2 and she's learning the rules and it's for her safety. However, at 2 1/2 she's more well behaved than most kids I see. We take her everywhere with us, but she doesn't behave like a wild animal. If we are at a resturant and she acts up, we correct her or someone is going to the car, we've done it several times, and when we ask her if she wants to go to the car, she knows we're serious. The other people are there expecting to have a nice dinner and I'm not going to allow my child to annoy them. She also doesn't run around in a store - any store - like a little maniac. If they aren't taught by the parents, they don't know any different. You want to give me a "look" because I corrected my child's behavior in public, go ahead, but don't you dare stick your nose in my business to raise a polite, well mannered child and expect that I'm not going to have a few words regarding your behavior as well. This, however has never happened, I have been, on many occasions, complimented (by older couples mostly) for how well behaved my child is.
My daughter loves to help mommy cook and bake and I let her, I'm hoping she's going to want to do it for years to come. But, when things are done and there's a cake - NO TOUCHING, and I only have to tell her once. But she's 2 so I tell her each time, sometimes she tells me, "Mommy I not touch".