As posted above, keep it warm, but let it be able to get off the heat if it becomes too much for it.
This last spring I found a 3 week old kitten on my moms garage floor. It had been there for over 24 hours and was cold/nonresponsive, there was nowhere for it to get off the concrete. As I put it under my shirt, it uttered that final sound that you hear before they die. I kept it there for about an hour and then drove home, with it still under my shirt to put it on a heating pad and hope for the best.
I put it on the heating pad, on low, and checked about an hour later. Not much had changed. I put my finger in a cup of water and dribbled it in the corner of her mouth. After that, it was an escalation toward recovery. I still have her, named Miracle, she is about 7 months old. Important, do not force food or water, dribble it in from the corner of their mouth. They will aspirate it into their lungs if forced.
This last spring I found a 3 week old kitten on my moms garage floor. It had been there for over 24 hours and was cold/nonresponsive, there was nowhere for it to get off the concrete. As I put it under my shirt, it uttered that final sound that you hear before they die. I kept it there for about an hour and then drove home, with it still under my shirt to put it on a heating pad and hope for the best.
I put it on the heating pad, on low, and checked about an hour later. Not much had changed. I put my finger in a cup of water and dribbled it in the corner of her mouth. After that, it was an escalation toward recovery. I still have her, named Miracle, she is about 7 months old. Important, do not force food or water, dribble it in from the corner of their mouth. They will aspirate it into their lungs if forced.