WEED SMOKiNG PARENTS?!?!?

I have a friend who smokes weed frequently in her home and so does her husband..It bothers me because she has a 3 yr old & an 11 mth old & they smoke it with their kids in the same room. Everytime she asks me to babysit I always do it no matter what is going on because I know thats one less day they have to breathe that. I love my friend to death but I hate what she & her husband are doing! And the fact that she smoked weed everyday while she was pregnant bothered me so bad to the point I hardly saw her because It would make me sick to watch her smoke & rub her belly..ughh! Any suggestions on how to handle this? Or something I can do?