I know a lot of us, myself included, are really hesitant about sharing our desires. I know it's difficult to bring up in conversation, but if you really want someone to know, perhaps you can take my advice:
Do NOT say something along the lines of "I'm an adult baby." I made the mistake of saying that to my sister (this was my first time telling anyone) shortly after I was caught buying GoodNites. It was a pain because she didn't understand what I meant, and I had to thoroughly explain everything, which didn't help my hysterical crying.
Instead, try comparing it to other fetishes. "You enjoy being tied up? Cool. I enjoy diapers." That's what works best for me, and it makes telling people a lot easier. If they ask why, I explain why. I explain that they offer me a feeling of comfort and security, and for insurance purposes, I always dispel the myth that DLs or ABs incorporate actual children.
I don't describe my exact fantasies, at least not the first time. If I weren't into this, I would be mildly alarmed at an adult telling me that he want a mommy to spank them, make them wear diapers, etc.
And here's the meanest and bitchiest thing: I find it much easier to tell people if I have something on them. For example, a friend of mine told me that he's into cross-dressing. I then felt comfortable telling him what I like.
I know that some people aren't going to accept it, and some are going to think you're crazy, and unfortunately, there isn't much you can do.