When a shed area attached to an older home in Hubbardston was torn down for renovation, six Gray Fox kits about two weeks of age were found in the "den" the mother fox had created underneath the structure. If forced from its den, a mother fox will create a new den and return to retrieve the kits when " the coast is clear." Upon the advice from Tufts Wildlife Clinic in Grafton, the owners created a situation whereby the kits could be easily found and relocated by the mother fox. The second night after the disturbance, she took five kits but left the sixth, which eventually joined other orphaned gray fox kits being cared for by a licensed wildlife rehabilitator in the Berkshires. Litters of four are more typical. It's likely that the mother fox recognized her inability to feed six kits; possibly the last kit would not have survived in the wild.
The MassWildlife website has a wealth of information about living with wildlife. See Living with Foxes as well as a life history fact sheet accessed via the same web page.