Just a thought I have never tried this bit maybe get a tiny fish hook and bait it with a piece of shrimp or something and put it where the crab is. When he starts eating slowly pull on the line pulling him out of his "hole". Do this with the lights out. I go crabbing all the time this would basically be like using drop lines for blue claws. When you get him out of the hole either you or your son be ready with the net. It works pulling blue claws from the bay so it may be worth a shot.
Edit: make sure it's a good size piece of shrimp.
And with Kevin’s method with the hook and shrimp, you will still want a pot of boiling water ready…..with a little Old Bay seasoning in there. Nothing better than eating that little devil once you catch him!
.