I'm going to leave them be. Two other people are feedign them, as I found food in the bowl I hid, and an empty cat food can in the dumpster. Found those the same day I found the kitten -- I think other people spotted them before me. Plus the mother is way too accepting and nice, so I think people who come out to smoke on their break from a nearby business, are bringing them scrapes. When the kittens become trusting, I suspect one-by-one they'll get adopted. Otherwise the whole area would have been infested with cats for years.