I bought The Age Play and Diaper Fetish Handbook by Penny Barber for my girlfriend. After reading the first chapter she told me that she knew all of that stuff and it was rather remedial when it comes to the fetish. I asked her to continue reading it and WOW, she said this explains so much about your requests, reactions, and mannerisms.
Since she started reading it she has engaged in this side of me on a regular basis and is actually showing much greater interested in the fetish. I have gotten to wear to bed every night and we have have changing time play. She has talked about getting a 50's dress with petticoats and it wanting to get more into the mommy role.
If you are in a relationship with someone and they don't totally understand this part of you after you introduced them or explained it to them I would recommend this book highly.