^ Hardly the same thing. Sofia was cast by her father in The Godfather III when it was clear she was out of her depth. She hasn't had a leading role in a movie since, though she has gone on to prove that she's a fine director.
Stephens hasn't appeared in any movies directed by his mother. He's won the Charleson and Gielgud awards for his stage acting. He's appeared in a variety of tv series, tele-movies and movies. You may not rate him as an actor but are you seriously saying that he won all of those roles because of who his mother is?
It's not like she's a major box-office draw, with some grasp over directors and casting agents, is it? If she was, then why didn't her late husband, Toby's father, Roibert Stephens, an acclaimed stage actor, get more movi leading roles?
And if he's only getting these roles because of who his mother is, then why isn't Jason Connery, whose father Sean is a much bigger star than Stephens' mother, getting similar roles?