Anyone know what breeds these might be?

[lindsaymarie675]

I bought this chicks three weeks ago at Tractor Supply. They were the same size. Now the one type is significantly larger. Anyone have any ideas of what the breeds might be? Also, will the ones that are getting bigger hurt the smaller ones?

 

[Vedwards]

The two black ones look like barred rocks. I don't know about the other ones. Can you get clearer pictures?

 

[lindsaymarie675]