I see older kids riding in carts in the grocery store all the time.

RE the standing up in the cart, this is a camera shoot for an ad campaign so we can't expect too much realism.

You may have something here, but I think it's a stretch/weak.

"a farmer is otherwise called a "picker" and children are sometimes called "pickaninis"

The term "pickaninny" goes way back and is a racist slur against black children.

https://en.wikipedia.org/wiki/Pickaninny

Good catch and good research