They probably will in a few more weeks. Last year when I had my RIR chicks, I kept them in the baby chicken cage for quite some time before I put them in the coop, as I also have older hens. So they were 3 months before I was able to put them in the coop, so thats how old they were before they roosted.
The first two weeks or so, everyone huddled and slept in the nesting boxes. I took the shavings out, but that didn't concern them. I was going to block the boxes, but before I could they figured out roosting.
Now, I have one Leghorn roosting on the pole that holds the water. Poopy water! I have to figure out a way to block the pole.
Just put the chicks on the roost by hand, after dark, if you want them all to get with the program. They are probably old enough now to learn. After you put them there manually for a few days they should get the clue and start putting themselves to bed.
To keep them off the waterer, hang something over it -- ideally something large, flat and tippy, like a bucket lid, but something fairly large and heavy can work too, so if they push it aside to land on the waterer it swings back and pushes them back off.
I'm having a similar problem. I have 6 chickens that are around 8 weeks old, 2 that are 12 weeks old and 2 adult chickens. none of them want to go in the coop at night. Its a new coop so I thought it may just take them awhile to get used to it. If I physically pick them up and put them on the roost the adults and the 12 week olds will sit on the roost and go to sleep, but the little ones will not.
All the little ones are sleeping in the doorway to the coop piled up on each other.
The adults will go in to lay their eggs, but sleep in the run.
Silly question, but are chickens afraid of the dark? do i need to put a nightlight in the coop? Its been pretty warm here lately, is it just too hot in the coop?
If your roost are low to the ground they will sit, up high they can not make it at 6 weeks old. My young ones do not roost until they are a few months old.
As was stated give them time, but also put straw on the floor for them to lay on.