What you are describing is perfectly normal. When they are chicks, they usually sleep in a group on the floor. They are not cold or anything like that, they just like the company. They will play on the perches during the day, but they are just not ready to transition to the roosts to sleep. If the weather is hot, they may spread out and not sleep in a group, yet remain on the floor.
At some point, one chick decides to actually sleep on the roosts. Within a very few nights, usually one or two nights but sometimes more, all the chicks are sleeping on the roosts. I've had broodies take their chicks to the roosts anywhere from age two weeks to four weeks.
I've had brooder raised chicks start roosting as young as 5-1/2 weeks, though 10 to 12 weeks is more normal. Some take even longer. My brooder raised chicks don't have anyone to teach them to roost, while my broody raised chicks do.
If you wish, you can start setting them on the roosts at night after it is too dark for them to see to get down. All you really have to do is teach one to roost and the others will soon follow. Or you can let them decide when they are ready. It's your personal choice. It really does not matter to the chickens.