A hen with one week old chicks (hers? right?) wouldn't be laying eggs already. Usually the hen doesn't start laying again until she's finished taking care of her chicks and told them to "get lost." With our hens, this was at about 5 weeks after hatch, and they started laying again the week after this. Do you have any other hens that could be laying their eggs in this hen's nest? That's odd, because a broody will usually fight fiercely to keep other hens away from her clutch.
Is it just the egg shells you're seeing? Or do you see yolk, etc.? If it's just the egg shells, could it be the shells left over from the hatching of these chicks? I know one of my hens neatly stacked all the eggshells from her clutch hatching with the top inside the bottom of each shell. That's one tidy hen.