I live with my parents and while my room has a mezuzah scroll (no case) my brother’s room has no mezuzah (he is below the age of Bar Mitzvah). Is it my obligation to make sure his room has a mezuzah?
Thank you for your question.
There is an obligation, at least on your father, the owner of the house, to have a mezuza, on all the doors that are in use in the house. Even a room that is only used for storage, needs a mezuza, definitely a room that is used to store things and used for sleeping.
If you need help getting a hold of a mezuza, I am willing to help you out.