A few days ago I posted a photo of a mother squirrel carrying one of her babies at a full run. Here is an excellent video that I found on YouTube that shows a squirrel retrieving two of her babies after they got separated from her:
Near the end of the video, the videographer stops the motion a couple of times so that you can see how the mother positions the baby. What is most impressive is that these baby squirrels, far from newborns, look like they are almost as big as the mother and yet she runs leaping across the yard and up the tree trunk effortlessly with each of them.
For a good comparison, imagine picking up your ten year old child, running with him in your arms across a large parking lot and then up the stairs to your tenth-floor apartment, and then going back to do the same with his twin sister!