You have to realize that if the impacts of second hand smoke from cigarettes has resulted in the restrictions on smoking, that the risk of brain damage to children is going to be a much greater threat.
The damage of lowered IQ cannot be undone. It’s permanent. Think of the potential for law suits and custody battles. Think of the potential for kids to sue their parents for permanent support “because you made me stupid by smoking pot in the house”.
So if the bureaucrats did something stupid once, we have to keep right on doing it? Why? That's the kind of rationalization that makes regulations multiply like rabbits.