I am in the same boat! The villhens came to us in March as day olds. half of them had poopy butts at some point within the first few days to weeks, and that seemed to destroy any trust they could have had for my hand. I was devastated.
Then, we learned that chickens are like men:
The way to their heart is through their stomach.
So, while they were still in the brooder at about a month old or so, I would crush up two of dried mealworms and hold it palm up. It took a little bit, but then it was like crack and they couldn't wait for more.
This is my son with them a couple of weeks ago. When I step outside and say "cheep cheep" they all come running like little chocobos wearing bellbottoms. It is fabulous!
They like to follow me around the yard and be generally nosey. But, they do not like to be picked up, with the exception of Roovirine, (The dark one in the middle trying to make his way into my kids lap.
We just got the new ones in this week, and OMG are they freakin cute! However, one of them turns into a psychopath if they see a red light, so we cannot use one. Her name is Evilene, the wicked witch of the west (side of the brooder). The first day she kept grabbing on to the others eye and would not let go, trying to drag it across the brooder. I even picked her up while she was latched on thinking she would let go, and it lifted the other chick off the ground! After switching out lights, she has been fine aside from an occasional peck, but they all do that. However, she does not like my hand at all at the moment.
I feel like I have started off badly and worry I wont get to have a cuddler out of these either.
I have been trying to find info on how young is to young for the treats and have been getting info from all over the place. But I figured by three weeks I will be doing the same thing as I did with the first ones, but extend the play time a little longer before they go out to the coop. I hope it works!
I am following his thread to see if it works out for you or any other advice that is shared. I would like a cuddly chicken or one that will ride on my shoulder like a parrot for Halloween (my long term goal

).
Good luck to you!
PS: They are all Brahmas, just different colors.