It kind of took a while since it was a gradually evolving thing for me, and had a pretty good ending. My first (or rather second) encounter was out of curiosity when I was around 4-5 years old. Some family friends were visiting from out of town and they brought along their two sons, one of which had issues mentally and had to wear a helmet and diapers. The older of the two and I were messing around and one day he suggested we try on a couple of his brother's diapers in secret, and being mischievous kids the thought of doing something we weren't supposed to was too good to resist. So, we snuck in one evening and each grabbed a pair from the case left open on the bed, then proceeded to try and put them on, giggling in the dark. One of the parents walked in on us, however I hid behind the door as my friend was dragged outside and presumably punished. I was able to get off scott free, dropping everything and quickly pulling up my pants as I made my escape. That marks the beginning of how I became interested in getting back, but there were some issues that kept me back.
A year or so later I was visiting another house of some younger kids, who were around 3-5 overall I think. The family was having some trouble at the time, and as a result the kids were still sleeping in cribs, though the sides were always lowered so they were more regular. They also had a well supplied changing station, and wanted to see the oldest of the current group, which was me at the time, diapered. After some convincing I gave in to temptation and decided "I'll try, but just one, no more than that." Can't say I've followed through with what I said looking back on it. The rest of the day was filled with messing around in cribs and pretending to be kids. After this little event I didn't really have a desire to wear, though the interest lingered. Then there was my teens.
My desires set in and I felt bad about what I thought was wrong at the time, so I looked to the internet of course. I found out that no, I wasn't alone, and knowing that gave me enough courage to go forward. Then there's a bunch of stuff in-between, but that's not really important. I was around 15 years old and conflicted. I wanted to buy diapers, but I didn't want to do so behind my parent's backs, or try to wet the bed and be dishonest. So, I did the one thing I could think of, which was simply to tell them. I told my mom I wanted to talk to her later in the evening, and when the time came it went surprisingly well. She was actually happy because of how serious I was, the whole day she had been going over the possibilities, such as drugs, sex, or pretty much anything dangerous a teenager could be doing. There was a bit of therapy just to make sure I guess, but after some rules were set things went pretty well, and I even got to learn how to better tell others about the whole ABDL thing in case I ever needed to. Afterward I got a job and have been free to pay for what I want since.