Spoon the pumpkin pie filling into muffin cups, then cover with aluminum foil and freeze.
When you're ready to make the smoothies, add the milk and yogurt to a blender. Pop 4 pieces of frozen pumpkin pie filling out of the pan and add them to the blender. (Save the rest of the pie filling for another time, or for a second batch of smoothies if one isn't enough to calm the hungry beasts.) Add the cinnamon and blend until the mixture is totally smooth.
Pour into glasses and sprinkle with graham cracker crumbs.