The only duplicates we have are two black cochins and as they grew they developed differences. The main one is the size of their comb. One is larger than the other and that is how we tell them apart.
Different colors of leg bands can help you tell the chickens apart. OP, do you want to know if your chickens are roos or hens? If so, their comb development might help. You can post pics and people will be happy to give you their opinions.
Ill do that ill post some pics later.. im looking to buy some hen but there kinda expensive where i live right now so hopefully i can get some hens or pullets soon
I have White Leghorns too, and when they got older I could tell by their combs! Some are huge, some flop right, some flop left, some are crooked, kinda funny really! When they were all in the tiny comb phase, it was almost impossible to tell them apart! I like the leg band idea too!