You should provide a heat lamp for them until they begin to feather out. If your weather temps are hot make sure they are not getting too much heat. Right now at 3 weeks old they should have about 80 degrees heat source, especially at night...during the daytime if it's 80+ as you have them outdoors already, turn it off.
They have their feathers and are going into that teenager look lol I can probably turn it off now.The nights are ok and as they have feathers they can keep warm. I turn it off durring the daytime as it's been 80+.