Ideally they should be in a mini coop within the main coop for a few days to a couple of weeks. I personally let my hen make the decision when to take them out and mix with rest of the flock. IMO the adults pretty much ignore very young chicks and they are fine, but of course you need to ensure that the chicks have access to starters food. I usually move their mini coop outside during the day with the door open.
If in doubt let mum make the decisions as she knows exactly what her chicks need.