Chicks roost sooner if someone (doesn't even have to be mama) shows them how. I don't train my chicks to roost, but they've always followed adults (or in my first batch, I had added started pullets that had been around other adults) up onto roost with no interference from me.
Without adults to show them, IF you want them to roost now, you'll need to manually place them on the roost at dark to show them that's where they should be. Conversely, if you don't want to bother with that, if you leave them to their own devices they should figure it out over time, but it can take weeks.