I would generally suggest that if you feel you are “doing it for him” that you are helping him too much. He must essentially dig for the clams himself. You can teach him how but cannot dig his limit of clams for him. It would be up to any warden on the scene to determine whether, in his or her estimation, the clams count toward your bag limit. Part of taking the clam is digging for it, so your son would need to do the digging. According to California Department Fish and Wildlife Captain Steve Riske, people have been cited for taking an over-limit of clams by doing exactly what you describe. It may be that if he is too young to dig for clams himself, he will need to wait until he is old enough to do so. Otherwise, you two can dig for clams together but they will all become part of your limit.
There is no regulation in California I am aware of that would prohibit anglers from wearing felt soles. With that said, we do encourage anglers to disinfect and sanitize their waders and boots in between trips to other non-connected watersheds. Although techniques vary in efficacy, I often tell anglers that freezing, if possible, and complete desiccations are better than nothing.
If your interest extends beyond California borders, this site has useful information: http://www.stopans.org/Felt_Bans.htm.