Mothers do move their babies from one nest to another, and sometimes leave them on the ground temporarily during transport. This is a photo of a mother moving her little baby by grasping it in her mouth:
If you do not see a destroyed nest, dead adult squirrel nearby, or threatening situation (such as cats, children, dogs, immediate threat of severe weather, or other dangers) in the vicinity of the baby, it is best to try to get the mother to come back for it.
You can attempt to reunite the mother and baby if it's still daylight (as long as the baby does not appear to be injured or ill). Be sure to look around the area and see if other babies from the litter are also on the ground. Typically, litter sizes average 2-7.
Whenever you make the decision to handle wildlife, you are doing so at your own risk. If you decide to do so, please follow instructions carefully, and take appropriate precautions. Do not contact wildlife with bare hands, and do not allow children or pets near baby wildlife!
Many wild babies may look healthy, but can harbor fleas, internal parasites, or illnesses that can cause harm if proper sanitation is not observed. Always wash hands immediately after handling the baby or its container, as well as any clothing or other item that comes in contact with the baby squirrel. Discard used disposable items away from where people or pets may come in contact with them.
To pick up an older baby, use gloves and a towel. Use protective eyewear. Older babies can deliver a good scratch or nip. You can gently pick up a very tiny baby, such as a newborn, with a soft cloth or latex gloves. Picking up a baby squirrel will not discourage the mother from coming to retrieve it.
Put the baby(s) in an open box with some soft cloths to contain them. Don’t use stringy cloths such as terrycloth, as the babies can get their little nails stuck in the loops. Place the box in a safe place near where you found the baby, or near where you think the mother or her nest may be.
The baby is defenseless against dogs, cats, hawks, curious children, etc. Stay at a safe distance, so as not to scare the mother, and wait to see if the mother comes back. It may take an hour or two. You can secure the box to the tree, but make sure the babies can't climb out. Even little ones are good climbers and can fall out and get injured.
If the mother does not return to pick up her baby after about 2 hours, or if it is getting dark outside (or severe weather threatens), you can keep the baby in a safe, quiet, warm spot away from children, pets, loud noise, etc. Then immediately locate and call a wildlife rehabber in your area. For what to do until you hear from the rehabber, CLICK HERE.