At 3 weeks of age you should expect a whole clutch (if you had that many chicks) to all be wadded up in the brooder with bloody heads.
Their little heads will be so bloody that they can barely open their eyes. A little baby oil or Vaseline smeared on their noggins will get them seeing again. After this they have decided who is the boss of who and run together peaceful until the little roosters get to about crowing size. Then they will do the whole thing again only this time without the pullets.
Young roosters or cockerels are unsure of their status and often either attack or are attacked by the females in the flock. The oldest or highest status hens are usually the last to knuckle under to the flock rooster. Just like dancing the tango it takes two, and any hen or rooster who refuses to acknowledge the higher status of another bird will be attacked on sight or at least anytime the higher status and lower status birds interact.
After all they are chickens and chickens only act like chickens. To try and bend, fold, or spindle a chicken into the shape of a little feathered human is in my opinion an inhumane act.