I have had a very similar situation. I was like 16 when it happened. I had my own car and was able to drive, so I would drive anywhere poeple didnt know me to buy diapers. I would then leave the diapers in the trunk of my car until my parents were gone and then bring them into my room. Well one day my parents "Cleaned" my room, out of concern for me. They were trying to find anything that might help them understand me (I was a wild child, deeply depressed, on drugs (been clean for six years though now), anti-social, etc). My parents didnt really know about my fetish, once in a while they would find a picture or something on our computer, but never really said anything becuase at that time, I was looking at tons of different porn sites, from straight all the way to extreme S+M and everything in between including AB/Dl sites. So yeah they never really said anything until they started finding more and more AB/Dl pictures on the computer. Then all they did was scream at me and ground me. Then one day as they were "cleaning" my room, they found an actual diaper and to go along with that they had found a notebook full of stories that I had written, and alot of those stories included diapers in some way or another. They didn't say anything at first. I knew that they had found it becuase when I went to wear the last one it was gone. A couple of days later though they did try to say something, well my dad did anyways. I was helping him in the garage and out of the blue he said something along the lines of, "Me and your mom found some stuff in your room." Me being the cocky ignorant kid that I was at the time said something to the effect of, "Yeah so, you guys have found lots of shit in my room." My dad was silent for aminute and then he mentioned the diaper, and I immidiatley closed up. He asked me why I had it, I didn't answer. He asked me if it was a sexuall thing. Thats when I walked away closing all line of communication.
When I closed the lines of communication down it brought two things, one being that later on in life I would look back at that and think to myself that I was a jerk cuase he was just trying to understand. Two the diaper thing never came up again, which I thought was a good thing, cuase I didnt want to talk to my parents about my sex life.
My point being is that if it doesnt come I would definitley let sleeping dogs lie. But on the other hand if it does come dont close the lines of communication. Your mom might be more understanding than you think. Let her ask questions and just answer them honestly. Keep an open mind and listen to what she has to say, see her side of things. Hopefully she'll see your side with an open mind as well.
Good luck to ya.