We took our kiddos out in public from, pretty much, day one. And we did it together the vast majority of the time. We wanted them to be exposed to public situations, and behave as expected, as early as possible.
Although, obviously, it wasn't always all unicorns and rainbows, I rarely remember tantrums in public, and only one full-blown meltdown (that I've posted about before), which was from youngest DD.
She was between 2-3 at the time. We were in Walmart and she wanted something that she wouldn't take no as an answer for. Just as soon as it got beyond anything we had ever seen from her before, I gathered her up kicking and screaming the whole way out the store heading to our car in the parking lot (that was why we usually shopped together, as it was my job to play "bouncer" in the pretty rare event that happened).
As soon as we got out the the door into a crowded parking lot, the little darling started screaming at the top of her lungs "MOMMY HELP! MOMMY! SOMEBODY HELP ME!!!!!"
Of course, everyone within earshot stopped in their tracks and thought I was some sort of sicko kidnapper (little stinker doesn't even cover it). I assured everybody that she was my daughter, I was headed to that white minivan right there, and waiting for my wife and two other children to finish shopping. Luckily, that seemed to satisfy everyone.
It was tons of fun getting her strapped into the car seat, as she continued melting. But, she never did anything like that again. She, and the rest of our kiddos learned at an early age (even our special needs son) that it wasn't right, we wouldn't put up with it, and nor should others be subjected to it.