Rat Moms & Baby Sharing

[hhw]

In one of my cages, I have 2 female rats together. One had a litter a few weeks ago, and the babies have been opening their eyes the last day or so. The other just had babies today. While she was giving birth, the older babies were swarming her while their mother was off on the opposite end of the cage, sitting around nonchalantly. Since it seemed like the older babies were stressing the new mother out, I separated them out along with their mother.

Should I have been worried and separated them, or should I just have left them together? It just seemed to me that the new mother had adopted all the old babies as well as having all the new ones, which would seem like way too much of a load on her. Or, is that natural, and the older mother would just help out with both litters kept together in one big bunch?