I introduced the four babies to their adoptive mommy, who has been broody for a little under two weeks.
She took them without hesitation, and this morning they're all peeking out through her feathers while she talks to them.
She wasn't paying any attention to me when I approached with the first chick. She hissed and puffed up when I lifted her wing and tucked the baby underneath, then looked around in confusion as it started chirping. Then she started talking to it, still looking confused, and finally looked under herself. Then she squirmed, puffed and purred.
I took out the eggs, tucked the rest of the babies under where the eggs had been, and she was contentedly chuckling when I left the coop.