Wildlife rehabbers are trying to speculate why some litters do so poorly and others seem to do fine- that is why you might find conflicting advice on the internet. One speculation is the affects of yard chemicals on the mother rabbit that is passed on to the offspring.
I had many young wild bunnies die- and I had proper bunny formula, pages and pages of info from wildlife rehab seminars, etc. That is why I only rehabbed for one summer. Then I got a pet bunny and will not bring wild bunnies into the house even though in the US I am not aware of any transmittable airborne diseases- but my house bunnies are treated like royalty and I am taking no chances- plus the heartbreak was terrible when I lost a bunny.
I colored in their white blazes with a paint pen in order to be able to tell them apart for feeding and monitoring purposes. Here is a pic of one of the litter- they are on real rabbit fur since the HSUS (Humane Society of US) takes donations of old fur coats and sends them to rehabbers to use with babies.
So I know how you feel- it is very sad to lose a baby bunny- but you did all you could and that is all anyone could ask for and more than what most people would have done. (I lost 2 of the litter below when I rehabbed them)

