Not too mention that a jumper in the US is closer to a pinafore.

Yes, I'm aware, a colleague moved to Berkeley and relayed a story where he confused a lot of people :)

I'm American and have no idea what a pinafore or American jumper is. I know a jumper is a hoodie because I lived in Australia a while ago. But that's not a word I ever hear here.

It's like overalls with a skirt. In the 80s they were popular for girls.