I'm sorry for your loss!
I agree about seeing pictures of your set-up. This is exactly what i do with my chicks, at about the same age, and have never had a problem. I set the feeder and waterer near the heated area at first, and move it out as they get comfortable running around the bigger space. It helps to spread some food under the heat lamp, with a trail out to the feeder at first too.
Do you have different bedding out there? A different feeder and/ or waterer? If yes, make sure they can recognize what they are.
Is there adequate lighting? Windows for natural light?
BTW, do you have your heat lamp very well secured out there? Mine is chained up to a solid bar or hook in the ceiling rafter, and tied, and the electric cord is also fixed up there, triple securing the lamp.
How are the babies doing now? Warmed up under their lamp? Do you have a thermometer under the lamp to check the temperature there?
Mary