When I raise baby chicks indoors, I always try to time it for nice spring weather so I can begin taking them outdoors to their chick pen in the main run to begin integration with the adult flock about the time they reach two weeks of age.
I have a small pet "taxi" that I originally got to transport my cat to the vet. I set the carrier beside the brooder, and load the chicks one by one.
When I get them to their pen in the run, I set it down, open the door, and leave them alone to venture out when they are ready. The first time it takes them a while to screw up their courage, and it's usually the boldest one that steps out, then the rest follow. I leave the carrier right there so they have it for both security and to return to if they begin to feel chilled. When all the chicks return to the carrier, it's my signal they are ready to go back inside to their brooder. No need to fear not being able to round them up because they will put themselves back into the carrier.
After the first week, they will zoom out of the carrier the second you open the door, racing around and even flying if there's enough room to get airborn. Their heat needs will be less and they will be able to stay outside longer before getting chilled. If they aren't quite ready to go back into the carrier when you want them to, all you need to do is toss a few meal worms into the crate, and in they will all zip, no problem!