Watch your temps...rats tend to do better in 70-80 degree tempatures.. any hotter and nurseing mothers will dehydrate and kill and eat the young for moisture and to replace the electrolytes they are looseing from the heat and nurseing (even with water present). If you suspect that this is the case, you can suplement their water with Pedialyte the clear sugar free kind, it's like gatoraid only easier on their systems with less sugar.
Hope that helps