They appear to be two different ages. I would say the one in the first picture is around 1 week old, and the one in the second picture is closer to 1.5 weeks old. Still a little hard to tell; besides, tractor supple gets chicks every other day to every two days, so they shouldn't be that far apart.
Honestly, the yellow ones do not look like australorps. Tractor supply does not know anything when it comes to chicks...or at least the stores that I have went to. The black and white ones are definitely black austrlorps, but the yellow ones look like golden comets, isa brown/red sex-link, or some other type of sex-linked chick.