I am not an expert on breeds but those look like meat birds. Hopefully others will chime in with thoughts. Meat birds do tend to have large hocks and can suffer leg issues. Most are meant to be butchered from 6-8 weeks of age as far as I know.
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Those look like meat birds...Cornish Cross.Here is some pictures of the leghorns
Leghorn and meat bird chicks are not infrequently mixed up at farm stores.We got them from Tractor supply