If you had two lamps on them in a small container bin, it is quite possible they did get too warm even though the temps are low. And like the others are saying now, if they are panting and laying around, they are still too warm. Make sure the lamp is raised enough off them so it is not scorching them, and also make sure they are able to get out of the heat if they get too warm. Temp should be about 85 under the lamp, but again, they should be able to move freely should they get warm. Remember, happy chicks are ones that are up and around, eating, drinking and talking lightly. If they are chirping loud and huddling - too cold. If they are panting and laying around with wings spread out - too hot.
Each week, raise the lamp slightly higher, this is how you keep them warm, but not too much so. Good luck and hopefully everything goes more smoothly now.