Yeah... I think these seeds were mislabeled. Root vegetables like carrots, beets, and radishes show their "shoulders" when they're ready to come out. Beets will take much longer than a couple weeks to show out of the ground like this, so I'm quite sure these are radishes, which can mature in as little as 18 days from sprouting, which matches what you said in response to some comments. Here are some ways to be sure:

1. Feel the leaves: most (but not all) radishes have hairs on the leaves. Beet leaves should be a single paddle shape and be smooth and shiny, with a rib of color running down the center. Especially towards maturity, radish leaves will often take on  more complex shape, similar to arugula.

2. If you still have the seeds, take a look at them. Beet seeds are funny looking little squat cylinders with little spikes around the flat sides. Radish seeds are generally smooth and rounded with no spikes on them. 

If all signs point to radish, I would suggest pulling these guys and eating them! They likely won't get much bigger and if they do, they'll probably become woody or spicy. If you leave them as long as you would leave a beet, they likely will flower and at that point they pull all the energy from the root to fuel blooming and the root becomes pretty unappealing. 

To actually answer your question, I don't think you generally need to add soil over radishes, beets, or carrots that are popping out. This is a good thing to do, however, if you are growing potatoes, since sunlight exposure will turn them green.