@Kiki if you are driving him home, it seems you have the right to ensure he doesn't have anything illegal with him or you might be in trouble, that's how I would put it to this boy next time you pick him up. Then make him empty his pockets, and go thru his backpack.
If his Mom complains, tell her you won't have anyone (police, etc.) thinking you are buying this crap for him and if she doesn't like it he can find another way to or from school.
Would you allow him in your car with drugs in his backpack? It is illegal for him to be in position of nicotine at his age.