Pretty good advice so far.
Beware of presenting yourself accidentally as aggressive or a threat... birds have instincts, body language and great eye sight.
All birds have unique personalities, some behaviors are inherited, instinct and others learned. Thus lines and breeds may react differently.
Treats combined with simple commands or sounds can help you communicate with them better. Yes you can train chickens to voice commands... whistle recall like a dog, or go in your house, or other things. They can be clicker trained, they can learn target training just like a parrot and more.
Patience, patience, patience... you are building trust. Let the birds work up the courage.
Calm, slow movements, slow breathing on your end can help.
Watch videos on training pet birds especially by people who emphasize understanding the bird versus imposing human will.
Koodos on changing brooder height or how to approach babies from the side, very true they are afraid of death from above.
An idea I plan to try is recording my voice & hubby's voice making calming sounds to play to babies when not around... try to impress the sounds of us on them while abscent this is a future experiment with next batch.
Study the sounds your birds make... try to learn happy versus upset sounds, this is a big indicator of if they like you even if they run away if they make a happy sound when you approach before booking it.
The following is for training pet birds but I found the advice can be applied to chickens... I found these guys useful in making me rethink my interactions with my chickens even though they are parrot guys. If you watch body language videos on parrots and then observe chickens you will see parallels... coop = cage. Keep in mind there is a lot of one on one training going on here, adapt as best you can.