Fighting chicks. Cockerels?

[Chichero]

my 3 week old Serama cockerel.. (red comb and wattles) is attacking only certain sebright chicks in my bantam brooder. Smudge will walk past other chicks to go after these 4. You think these four are cockerels too. I moved them into another brooder and all is well again.

 

[Swastik Choudhari]

Not necessarily cockerels.
Post their pics.

 

[Jetblack2004]

He will pick on any chicks, whether they are male or female. He won't bother picking fights with the male chicks until they are much older.