I’m so sorry another has passed, I know you’re doing everything you can for them. It’s just so hard to watch when you know the outcome is probably not going to be as good as you hoped.
I’ve read where many rehabbers put a heating pad under a towel so the babies can maintain their body heat.
I think they set it to medium but put it so it covers only half the box and cover with a towel. That way the babies have a choice of crawling toward it if they’re cold and crawling off if they’re warm enough.
I wish I knew more to tell you, I want to take the cottontail rehab class next spring and learn more.
I know you feel bad, but remember the last lines in that article I linked to about wild bunnies:
“Remember that it is not the destiny of more than a few infant bunnies to survive to maturity. If it was, the World would be over-run with rabbits.” I know it doesn’t make you feel any better, but it has a lot of truth in it.
hugs and thumps for all your hard work, Kathy