My parents definitely know I smoke, at least my mom does, though I don't see her knowing and not telling my dad.
I've been high around her so many times and I'm pretty bad at playing sober, one time she was even joking about how my eyes were totally so red because of hey fever and stuffs. Apart from that though they've never really said anything.
They are kinda ok with it though, I mean all my other siblings (and my parents themselves (who have done even harder drugs)) have smoked up, guess they see it as something for me to figure out myself, just like drinking.
I'm cool with that.