Nicole & Susan, yes heat shields are used after babies are born – think about 4 or 5 chicks growing bigger in that small box and in the heat of summer. I am not sure about putting it up after they are hatched (most of us have it up when we just get eggs). Like Nicole said, If your box is in full sun in a hot area, I would definitely have up a heat shield, and they still have about 2 weeks before fledging. It is put on the top, south & west sides of the box – of course not on the front. Spacers are critical, otherwise you just keep the heat in and with spacers you have a dead-air space for the heat to flow through & out. Give it some thought, but you need to do it quickly if you are going to. Again, you have a brave mama – papa is gone and in the past, but you have a chance to help her. Good luck!