Great advice from Norachan! The Zithromax has helped the other kittens from that batch. Can you tell if the kittens that died are all from the mama cat's natural litter? If so, it could be something specific to them, such as chemical exposure (the mama cat may have been forced to drink contaminated water or sought shelter in a contaminated place - homeless pregnant cats have it VERY rough until a kind soul brings them in). Also, keep giving some pedialyte at a ratio of 50/50 to keep the electrolytes balanced. Do you have probiotics to give them? A good quality plain, unflavored WHOLE milk yogurt fed at least 2 hours (I do 4) before or after the antibiotic dosage is an easy way to add probiotics; you can up the probiotics dosage by sprinkling a capsule's contents on or in the food.