I believe that they are chicks until they feather out...then the females become Pullets and the males graduate to Cockerels. The Cockerels elevate to Rooster or Cock once they are a year to a year and half old; and the Pullets become Hens once they have begun laying. But even when the Hens are first laying; their first couple months of eggs are still known as Pullet Eggs.
I also have a non-standard term for them as they grow-out. Once they are in that awkward inbetween phase...when they are not fully feathered out....when they are all fuzzy and also have itty bitty feathers...I call them "Ragamuffins".
Here's one of my Ragamuffins from a few weeks ago.
I'd say technically they are still chicks as long as they are still "pullets" and "cockerels"...then at a year they change to big kid status. My birds are still my chicks, even though the oldest are almost 16 weeks old. (And the Cuckoo Marans pullet is HUGE, with this honk-cluck that makes me call her my Bea Arthur bird)