If they were 6-10 years old, I'd make it very clear that it's wrong and very bad!
11-14, what the hell?! that stuff will mess you up doods, its why we have vidya games...next time i'm gonna kick your ass, maybe some drug tests!
15-18, oh shit...there isn't much i can do, but don't be scared to come home high...but be very careful of your decisions, stay away from those other drugs at all costs.
19+, hey! corner that...don't be an ass, i'm your father!