We have a potato answer!

Long story short, my boys go to a technical institute. They’re very smart and the school got us in under special funding yada yada gifted kids etc. Anyway, so apparently they’ve been studying electricity and batteries and also renewable resources.

The potatos are from a bag the boys brought home from school, that they  a. turned into batteries, b. tried to make Glados from, and c. were going to see if they could start a potato crop in the back yard to make constant renewable energy. Or evil computers that can’t do much but sass at you. Either way, the potatos have been found!

This is an even better explanation than magically-appearing-potatoes.