I'm in GA, USA.
I don't think they're motherless. I pulled them out and tried to warm them up. Their stiffness went away but they haven't moved. I reckon they really are dead.
Like I said, they were fine last night. It got down to 38 during the night last night/this morning though. I fear the plastic bag I put over them to keep the frost off also kept the ground underneath it from being warmed by the sun. :/
There were three of them. Do rabbits breed throughout the year? I'd hate for momma bunny to have to wait till this winter to do it all over again. I feel do bad! Live and learn, I guess...