Baby porcupines are born in early spring. They are born fully developed. The quills are soft when the babies are born, then harden within hours.
Until baby porcupines are big enough to climb, mothers will leave them on the ground while she feeds in trees. If you come across a baby porcupine in the woods that appears to be healthy and uninjured, and there is no dead adult porcupine in the area, assume that the baby is fine and does not need to be rescued.