I don't think the black one is an Australorp. Both australorps we've raised have had a good deal of white at that age! I would NOT say Australorp.
Here's our first one at 4 weeks (far right)
and 6 weeks (second from the bottom)
See all the white?
Here's our first one at 4 weeks (far right)

and 6 weeks (second from the bottom)

See all the white?