What is this?
It's difficult to tell from the photo, the shape and structure of the leaves are not as visible so it is difficult to tell. It rather looks like a potato, but I cannot say with certainty that's what it is.
That is a better picture and the leaves definitely look like potatoes. Probably tubers that did not get harvested and these are volunteers. If these are currently growing, you could leave them in the garden and harvest about September to see what kind of potato they are. At this time of year, they won't have any tubers or if there are some, they might be about dime-size.