AgreedAt 3 to 5 days old it's really too early to be able to accurately 100% sex them. With barred rocks you can take an educated guess based on their head spots and the wash down their legs. Females have a more compact head spot and a darker wash down the legs, while males have a more scattered head spot and less wash.
As they get older, there will be a clear visual difference between males and females. Since females are single barred and males are double barred, males will appear much lighter in color than females.
My girls are now 7 weeks old! Here's a few updated pics!The bird on the left is the most likely cockerel suspect, but it's really not screaming male to me. Can you get a pic of that bird's legs from the front? If it's got dark color down the legs, it should be female. The middle and right birds look female from the head spot.