Thats a hard one there.I was in the same situation but with alcohol with my 15 year old nephew at one time.He came to stay with me for 2 weeks.We had alot of fun and i let him have a few drinks he begged me and i put a cigarette in his mouth (not lit) and a beer and took a photo and sent it to my brother (his dad) hes a bit strict in that way it was all in fun.I still have those photos and they are one of the greatest memories of my life.He is about to turn 18 he has been in hospital since he was 16 from a car accident and doubt he will ever eat, walk, talk, laugh ever again.All he does is lay in a bed all day in the brain injury unit and soon has to go to a nursing home.He was my lil man i loved him so much and still do he was born when i was 10 and i am so happy that i let him do that with me being his aunt i knew he was protected and now that is one thing he will never ever be able to do again.Off this subject now do what you like with your cousin its your choice