Studies have shown that the high calcium content of layer feed harms chicks' kidneys. Your birds may seem healthy and happy, but just because the damage is not apparent, it that does not mean it's not happening.
Here is one of the studies and results:
http://www.pvj.com.pk/pdf-files/24_3/113-116.pdf
It's better, when feeding a mixed age flock of layers and young chicks, to feed an all flock, or grower feed and offer calcium supplements free choice on the side. In my experience the chicks and cockerels in the flock do not eat the supplements and the hens help themselves to the supplement as needed.