So sorry to hear this, is it possible your husband has some issues he needs to address?
Sounds to me he was trying to get your child to think "mommy is doing something wrong", by him asking you "what are you doing to him"?
I may be off on this thought so please pardon me, it was just something that crossed my mine as I read your post.
I get a small impression your husband may be a controlling guy? You say maybe it is good the kid is getting to see hubby's true colours, but it would be ashame if this tension continues for the kid's sake and you both.
I do not know the answer, but would suggest you talk to a therapist as to find out what to do to help nix this behaviour, communication skills, or if your husband needs some counseling, anger managment?
Just sending you some hugs and ideas from the "think tank" to roll around

(((((((((((((((((((((((( gloria ))))))))))))))))))))))))

In giving advice seek to help, not please your friend
SOLON