I remember a european skinemax film (maybe Italian) with a redhead maybe in her thirties (still hot though). She was a stepmom or something. The boy in it was infatuated with her. He drops his fork on floor in one scene just to go under table and look up and then reach up her skirt. He washes her back and front in bath in one scene. And in a scene where she tucks him in bed, he waits till she goes to kiss his cheek and full on french kisses her. It was one of the few movies from my child hood always wanted. Would like to know the title after all this time.

I think the movie you are looking for is called Malizia (malicious in English). I remember seeing this film on HBO around 1981. There is info about it on Imbd.

I had considered this movie as well. But it only involved one stepson. And he was much younger than the son in Malizia. And the dinner table scene was not panty removal. It was the kid dropping a fork just to crawl under table and dare to run hand up her skirt before being caught and admonished.