I feed mine Nutrena medicated Chick Starter/Grower until they merge with the rest of the flock, which is always fed Nutrena All Flock. Medicated chick feed does no good if the chicks aren't actually on the ground, as it helps them build resistance to cocci. If you stop the medicated feed before they've been on the ground, there is no immunity built up. It's one reason why I have a grow-out pen inside the coop - called Chicken Kindergarten - so the kids get their medicated feed "on the ground" and the older birds don't scarf it up. After I open the gate to the Chicken Kindergarten, I finish the bag of medicated feed. The older hens will go in there to scarf it down when they can, and the young birds will also eat the All Flock pellets out in the rest of the coop area, but that's okay with me.
I don't feed layer feed at all, because I have birds of all ages in my flock, plus ducks, geese, and of course, roosters. I do keep crushed oyster shell out 24/7 in separate dish, so the layers which need it can take it. The babies will taste it, maybe eat some, but not enough to harm them. Those layers which feel the need for calcium will eat the crushed oyster shell.