Full Grown hens - Crows won't cause harm... maybe attempt to haze 'em away from their feed - but that's it. Now they WILL steal eggs if they can get to a nest-box, and they WILL steal chicks. They do this with other birds, too - so Crow doesn't see any difference with your chickens.
I haven't had my bantams messed with, even though they're smaller - but they run with the turkeys and guineas - that get safety from their "bodyguards".
Like the others said - Crow will make Hawk think your yard is a bad Hunting Ground.