I agree they need that hest lamp.I cant imagine them doing them vey well without a heat lamp. Maybe inside after a few weeks of life...but not as day olds. I would highly advise having a lamp. First week of life needs to be around 95 degrees. In the coop with their mother, the mother would sit on them to keep them warm. The heat lamp takes the place of their mother.
Plan on them outgrowing that cage REALLY quick! I put 6 in a cardboard box a little bigger than that they are about 2 weeks old, they already need something bigger. So I will be working on that tomorrow.