I would say they are sussex crossed with legbar if they are a first generation cross between two heritage breeds. otherwise they could have some polish or anything with a crest somewhere in their background.
I love legbars and have crossed them over a few other heritage breeds and want to share the results (and would LOVE if others shared their results too). When i started crossing my legbar it was really hard to find images or what the babies might look like so i imagine there will be others out...