This video from the USA says about itself:
Orphaned Baby [Grey] Squirrels Rescued – A Documentary
15 October 2017
Mother Squirrel is missing and her two precious baby kittens have climbed to the nest box entrance and were calling desperately for their Mom. I was watching them in person and on a nest box camera so now it was time to rescue the little ones and take them to a wildlife rehab center I had coordinated with in advance. This is their story.
Mother Squirrels are some of the most dedicated in the animal kingdom and squirrels have very strong family bonds, you can sense the bigger older brother concern for and care of his smaller younger sibling.