Naw, I'll bet he's right. Carpenter bees are voracious little buggers that will keep coming back to the same place over and over again. This spring was bad around here for them. They were so thick out in the barn that it was like big flies around a pig sty.
I know of nothing that will deter them. It sounds like you are doing about all that can be done and that is killing the adults with an insecticide and putting poison in the holes. Leaving the holes open awhile might draw more bees into a poisoned hole, I don't know.
The mud daubers patch up the holes here about as fast as the carpenter bees make them. Those two species make some mighty interesting engineers. Both are as anal as can be about the perfection of their work.
You might try giving the kids a tennis racket and a BB gun.