It's a Monark Silver King Roadster for girls made by Monark Battery Co., in Chicago, Illinois. The company was in existence between the early 1930's and the 1950's. It's made of aluminum alloy, hence why it's probably lasted so long. Here's a history of the company I was able to find online. It looks like the example your found looks better than the one in the picture from the museum. Who knows? Maybe the museum would love such a pristine example of this piece of history.
https://www.madeinchicagomuseum.com/...k-silver-king/