They look like sunflower seedlings, birds sometimes plant seeds from feeders for future feeding but never remember where they plant them and they voluntarily grow.
It may just be a random seed by a bird, but wait until the end of May for more clues due to the small size of the seedling... sunflowers are very similar though and if it is, there would be a seed husk close by the plant.......
If you can dig them up and replant them in a area and let them grow it would be interesting to see what comes of them.
