I had never heard that before so I looked it up on about six different sites, and not one said the dress was pinned just the apron.
I grew up not that far from Lancaster, PA, but I had never really been a tourist. So , last summer when I was in PA we did the tourist thing and went on a tour of a so-called Amish farm. They showed the dresses and gave us the whole talk about the type of dress at various ages and showed us how the dresses are pinned on.
They prepare the dresses the night before, pinning the apron to the dresses and putting the pins down the back. It requires help in the morning and sisters help the younger girls.
The don’t use buttons, snaps, or zippers on girls older than 4. The men, however, can use buttons. I think that the Mennonites do use snaps or maybe even buttons that are covered. They do it for an entirely different reason.
We were shocked at some of the Amish practices and the meaningless restrictions. They use electricity in their barns they own business that require machinery and trucks, but they hire what they call, “Englishmen” to drive the trucks and run the machinery. The compay, Sauder furniture, is an Amish company.