I finally saw them. There are 3 baby squirrels playing in the tree now. They are about 7 inches long including their tails. I don't think mama will let them out of the tree yet but they scurry and bound all through their arboreal playground.
Apparently I have done a good job feeding mama. She is so fat that you can see the fat rolls jiggle when she moves. She is ready for winter in spite of the fact that she has been nursing 3 little ones for the past two months.