Firstly I noticed that four had grey legs and two had yellow legs but otherwise they were identical. What did that mean? Trawling the net gave the answer. Pure-bred Sussex have grey legs - add a bit of mongrel chicken and the legs are yellow. They grew a bit more and some started to develop combs. I still hoped for hens.
One suggestion for telling the difference was their response when you throw a hat above them. Males will instinctively look up to meet the danger and females will crouch down. They all crouched down. Maybe I was lucky.
Then three started to get taller, have bigger combs and more upright tails. Could these be roosters?
More research proved inconclusive. While these characteristics are more often male ones, in Sussex chooks it does not mean anything. So how many are hens?
Then I found a more definitive answer. If you look at their 'saddle' feathers - those below their 'hackle' feathers the males have pointed ones and the females more rounded.
Rooster with Pointed Saddle Feathers
Hen with Rounded Saddle Feathers
The final answer - three rooster and three hens.