There's two parts here: a.) What would I do, as the parent, if my child were to throw a tantrum, and b.) How would I react, as a parent, to another child throwing a tantrum.
For A: As stated, I would leave immediately. I'll hedge that a bit and say that getting to the point where a child is rolling around on the ground is a failure for everyone concerned, so ideally we'd never reach this point in the first place. If there's a disagreement, my kids and I can talk it out without resorting to a tantrum.
For B: I don't care what you do with your kids. In public at a zoo in an open area, have at it. It's a tough situation all around and I'm not going to make another parent's day worse by saying anything.
For A: As stated, I would leave immediately. I'll hedge that a bit and say that getting to the point where a child is rolling around on the ground is a failure for everyone concerned, so ideally we'd never reach this point in the first place. If there's a disagreement, my kids and I can talk it out without resorting to a tantrum.
For B: I don't care what you do with your kids. In public at a zoo in an open area, have at it. It's a tough situation all around and I'm not going to make another parent's day worse by saying anything.