Really liking this thread, my kid just turned 3 and not sure how to broach it. In CO so I really don't have any legal worries. The question of the tent has come up...just said it was a tent. Unfortunately that is not a good answer as he wanted to camp and/or play in it. He also asked about what that bright light is when i forgot to lock the basement gate and he followed me down, just had to say plants:)
Illegal states, do what you gotta do. I don't think that "family secrets" or anything like that is the way to go though. That's the shit molesters tell their kids. Alcohol doesn't get the same weirdness, my approach is to just treat weed like a normal thing that is for adults. Regarding it growing in the house, its just plants till they get old enough to know what it is or inquire. At that point, well, i think that is where just treating it like a normal thing for adult use comes in.