Tomato seeds begun in cell packs

Today I planted two tomato (stupice variety) cells with 2-3 seeds in each cell tray. I don't have any grow lights so I kept them in the warmth of the kitchen window with the clear plastic top on to keep them warm. My two year old son James was my "helper" and very excited about the garden. We didn't have any seed starting mix so I just used potting soil for these two since he was so excited about planting them. We already had the cell packs from a previous gardening experiment a few years ago that my wife had done so there was no (new) cost associated with these.