I think it is a type of Chenopodium, perhaps Chenopodium album. There seem to be native ones and introduced ones.

Most people consider this to be a weed in the garden. Surprisingly it can get quite big by the end of the season (I've seen it over six feet tall and with a very woody stem at that point).

Here is a link that might be useful: Lamb's Quarters (Chenopodium album)

These plants grow all over the New York City metropolitan area.

I'd always heard these were edible, and finally tried them a few years ago. Cook and use like spinach--tastes similar but better, with no bitter undercurrent like spinach can have. Somehow, knowing you're going to eat some makes the weeding go easier! Epazote, an herb good with beans, is another species of Chenopodium, as is quinoa.

Sure looks like young Chenopodium album plants. I don't think anyone would intentionally plant them unless they were big into wild edibles. Around here they are a very common weed, especially in disturbed areas. Most experts consider them an Eurasian species that came to the U.S. long ago. A few think there may be native varieties of the species.

My family has eaten this plant forever. My father used to make a sauce with it. It grows everywhere in Kansas and people treat it as a weed. I let one grow all year and it grew huge. I find them tastier when they are about ~5 inches tall. Mexicans call it "quelite".

Thanks guys.