Be careful with putting pregnant rats together. They can eat each others babies. It really is not a black and white answer. I keep my female rats that are pregnant in a seperate cage by themselves and up until the pups are weaned. If you put baby rats in with adult or sub adult rats they could eat the babies. I have had sub adult/adult rats eat baby rats even when they had fur. I wait until my pups have their eyes open and have a nice set of teeth so that way they can defend themselves if another rat tries to eat them they will be deterred from doing so.