Probably no one would ask your religion, so I wouldn't worry about that. If you were the child's guardian, you might try taking him to UU, their religious education actually teaches facts about the world's various religions. Since you aren't the child's guardian, you have no say in his reliigious education, and you should keep that in mind. You gave up any chance of having a say in his religious education when you refused to be his godfather. However, you are well within your rights to render your opinion honestly if he asks you questions.
I'm not anti-Christian. I'm anti-stupid.