When Buckeyes are young (under 7 months old), they usually appear lanky, gamey, long legged as the ones pictured. Sometimes a male will develop later and some earlier -- but for juveniles, they look like they should. They will fill in as they get older.
Also, if Buckeyes aren't fed a high protein starter their first 8 weeks or so, they won't grow like they should -- they can still be nice birds but for optimal development they need a >28% protein starter. And all that said, there will be still be individuals in a group that will far exceed the others and as well. there will be those that don't thrive as well -- no rhyme or reason to it, just individual genetics.
To me, they look like they should. Without hands-on, I cannot discern anymore about them at their age.