I just put out 10 6 week old chicks last night as well. No heat. I give them an insulated box bedded with shavings to sleep in and they tend to use it for about 2 weeks until they start to roost at night instead of sleeping on the ground. The ground is cold and will suck a lot of heat out of them so getting them off the ground and providing some type of barrier that traps the heat they generate will keep them warm. I give them the box to hide in from the adult hens and give them an opening that is only big enough for them to get through.