You can see the barred rock a little more clearly here. Here's the father:
Couple of key differences. Notice the color of the ears on this bird: the ear color is the egg color that a hen of this breed will lay. So this is a white egg-laying chicken breed. His son has red ears -- brown egg laying breed. The father weighs about 4lbs liveweight -- and the son weighs about 6lbs, so in addition to the brown egg laying trait the son has gained some size.
The father is looking a little ragged. This is year 2 for him, so he's due for a molt.