Chicks are chickens, just like puppies are dogs, kittens are cats, etc. "Chicken" is the name of the species: https://en.wikipedia.org/wiki/Chicken#Nomenclature

If you'd said "hens" you'd have a stronger point, but then you'd need to be talking about chicks and hens (and they could still cross whatever adulthood threshold you like within the week, as you didn't specify how young they are - "new" could just mean new to the farmer).