Well a pencil is soft wood and if it is a 12 ga then they must be tight but if one pencil could be made slightly smaller then they should come out. A pencil isn't that long so if you were careful and ran a small drill bit into the pencil end it might chip away at one enough to dislodge them especially if the gun has a choke which is only a couple of inches. It is easy to remove the barrel on that gun so I still would try to back them out with a dowel. Unless your son put them into the gun then pushed against the floor with a lot of weight it is hard to understand how they could be in that tightly. Have you tried to grab one of the pencils with a pair of long nose and twist?