That is the general rule, but these two were "hatch mates" so they are okay together. Stripey is definitely not the boss of the barnyard, but he does have a couple of hens that are his "girls." There were seven more eggs that Eggatha was still waiting on. I isolated her and the babies using a barrier. They had already gone through 1-qt jar of chick starter food when I went to lock everyone up last night. I have these feeders that are inverted quart jars attached to a little feeder thingy. I brought out a 2nd full jar when I locked them up and will fill both up again when I let the adults out in the morning. Chicks eat a LOT. Once I know she's "done" trying to hatch more eggs, I will move momma and the chicks to a brooder so they are isolated. Thankfully at this time of year, momma will provide heat and I don't have to string up lamps.
Addie--you would have loved to have seen the two "eyes" peeking out from momma's feathers at me. Two separate chicks, both checking out the "Big Chicken" when she brought food and water.
These babies will not be raised anything like those that are raised in battery farms. Their momma will be with them until they are able to join the others in the yard. She will teach them how to peck and scratch, how to perch, how to dirt bath, how to hide from threats in the yard, and how to go back in at sundown. She will be followed by these chicks for a good 4-5 months before they declare their independence. The babies will form their own little "mini" flock within the flock.
Momma is the best incubator. And a lot easier than a tray on a shelf. Broody hens flip those eggs 30x/day for something like 16/17 days. And, about 24 hours before those eggs hatch (Momma knows, she can hear the peeping), she starts to make a "purring" noise to help guide them out of the shells. I don't think a mechanical incubator does that. My hatch rate has been 100% in the past, we'll see what it is this year. 
Who knew having chicks was so much fun!! Love watching the babies and Momma.
