Toddlers embarrassed us in the store and my wife got angry because I reacted

Just yesterday, my wife, our kids and I went to the store. We let our 12-year-old daughter go alone because she wanted to search for some snacks. We were left alone with our 5-year-olds. As we were walking, they grabbed things from the shelves and proceeded to pretend to read them, which is okay, nothing wrong with that.Next thing I know they are grabbing every single cereal box off of the shelf and dumping it on the floor. One of them hits the other on the head with a box, so she starts crying and people start turning around to see what's happening. My wife tries to calm her down and I yell at the other.After that, when we were paying, the daughter that hit her sister on the head grabs the bag and because it's heavy, she drops it and a jar breaks. We had to pay. In the car, I was yelling at my daughter for doing that while my wife was yelling at me. Our 12-year-old daughter was likely not aware of the yelling because she had her headphones on.My wife said that she's a kid who needs to be taught behavior in public places in a calm way and that all kids do that, (I saw plenty of younger kids in the store and none did that) but how could I be calm if she repeatedly hit her sister on the head with a box?I seriously need advice on how to deal with this in the future. via /r/Parenting http://bit.ly/2Qe1Xae