To begin with they were fed on wet chicken cat food but later they had a mixture of wet and dry cat food (again, just chicken). They were all, obviously, too low in weight to be allowed to hibernate but some were really so tiny. Used to have to weigh weekly and keep a chart of their weight-gain!
The rescue I used to help has moved from my village and now has a large purpose-built hospital, but unfortunately it is quite a distance from here.