When there is nothing left for you to do, you have to open the door. Baby squirrels don't last forever.
If you've done your job, fed them, sheltered them, healed their wounds as best as you could, watched them emerge into healthy wild animals, an open door, a hatch swinging wide, is the only thing left you can give them now. The baby squirrels are long gone; in their place are juveniles, grown and growing impatient.
Open the door. Freedom rushes in at them like a deep breath they've been waiting their whole lives to inhale. It fills them.
Open the door. Let them come flying out or - in this case, strolling out, matter-of-factly. At whatever speed they choose, they will still know what to do. They are following a map that has been etched into their bones since birth.
Say goodbye. Love them from a distance. Don't forget them, though that favor won't likely be returned. And as you leave the woods, empty-handed, move on. Close the door. They already have.