When mine were that age, I put a 1-2 in diameter piece of tree branch in the brooder to hop on, play on. As they got older, maybe 4 weeks old, I put a piece of 2 x 2 across my tub (my brooder was a spare bath tub). I had to use duck tape to secure it, but it worked
Now they are nearly 9 weeks old and slept on the real roost in the "big girl" coop last night for the first time, proud mamma! I had to block off the nest boxes as they wanted to sleep in one of those.
Ok you can do this, however if you end up with crooked keels on your heavy breeds ( Sussex, etc.) that will be the reason. The keel ( breastbone) is still soft cartilage at this point. If the chick is perching and resting on it, and the keel is resting on the roost, it can grow in a crooked fashion. I don't know about bantam breeds, however in the heavy breeds like Sussex, it I best to wait until later to show them the roost. A good time is about 6 weeks old. Crooked keel will ruin a show bird. Plus is unsightly and unnecessary, tho sometimes it is genetic.