Yea...DS had to use his US passport when going to the States, and had to use his UK passport when we returned to England. Even though I have the correct visa for the UK, DS is not listed on it since he is a British citizen and therefore would not be allowed to enter the UK without his UK passport.
Similarly, he would not be allowed into the US with only his UK passport - if he was travelling alone with me. If we were with DH, it wouldn't be a problem, apparently.
This is actually only half correct. The US requires a US citizen to enter and exit the US on their US passport, the UK does not. We have entered the UK on my kids US passport (long story, even though they have UK passports as well) and it is not an issue. We have British friends who live in the US, kids born here, never applied for their kids UK passports, and they travel multiple times a year with their parents (who ONLY have UK passports) to the UK and have never had an issue entering on their US passport.
I realize your point was in reference to the visa aspect of it, which is a different situation.
Also if your husband traveled in to the US with your son on a UK passport that would technically be illegal.