unknown plant in my garden

[rafiwinters]

I just took this picture in my garden and wonder if anyone knows what this is? A Google image search isn't working well. What are these plants, how invasive are they, and how do I get rid of them?

ETA: I can't seem to get the picture to load right, so here's the description: a short seedling with two butterfly-shaped leaves. Lots of them in my garden. Any notions?