My realizing i was into wearing diapers and acting/being treated like a baby came from an early age.
The earliest was when I was about 4, my parents and I went to my Aunt's house and while walking around, I went into my cousin's room, who was about 1, so she was still in diapers. On her dresser, was a stack of girl's diapers (this was back when not only were baby diapers designed by gender, but they were also plastic backed). Curiosity got to me, so I took one into the bathroom and put it on. I wore it up until we were about to leave, where I took it off and threw it away.
After that, there was one major incident that made me come to terms with my interest. During summer time, up until I was 10, my parents would leave me at a daycare every day during summer vacation. During one of those times, when I was 6, I once again got curious about diapers, so I snuck into the nursery part one morning and took a diaper from the changing table. I then went to a bathroom that wasn't used during the mornings. After putting the diaper on, I decided to look at myself in the mirror. I couldn't figure out why at the time, but seeing myself in the mirror, where only a shirt and a baby diaper made me feel happy. After this, I would start occasionally sneaking more diapers out of the nursery to wear for the day. One day, after changing into the diaper, I felt the need to pee. Rather than just use the toilet, I thought "Well, since I'm wearing a diaper, I might as well use it." So, while still sitting on the floor, I peed the diaper. Now, sitting on the floor, again in just a shirt and a now very wet diaper, I felt just as happy, and instinctively, I started sucking my thumb. This would continue through the Summer, and I managed to never get caught.
At least, until the next Summer.
I guess the caretakers were noticing that diapers were going missing in the nursery, so they were keeping track. At the beginning of the next Summer, I had taken another diaper to put on, and immediately used it. However, after I had finished, the bathroom door opened and to one of the caretakers standing there, seeing me in a wet diaper, sucking my thumb. I was immediately dragged out, brought into the room that the rest of the kids were at in the morning, and was thrown over her knees, and given a hard spanking while still wearing the wet diaper. After the spanking, instead of being allowed to change into my regular clothes, I was changed into a fresh diaper, and kept in just the diaper and shirt for the rest of the day. To say I was being teased by the other kids is an understatement. At the end of the day, my parents were told, and between them and the caretakers, they came up with my punishment.
Since, they figured, I was putting on and using diapers, they said I must not have felt confident in my potty training, so said I would be kept in diapers through the summer while I was "re-training" to use the potty, and that I would be kept with the toddlers in their play room. I was told that I had to tell a caretaker whenever I needed to go potty, and that if I missed using the potty, I would get a spanking before having my diaper changed. However, they apparently having no intention of letting me go when I needed to. Whenever I told a caretaker I needed to go, they would "ignore" me and tell me to go play. The only time the would let me go is if I told them I had to poop, and even then, they wouldn't let me use a regular toilet. Instead, I was made to sit on a potty training toilet, with my diaper pulled down to around my ankles. However, when I didn't need to poop, I was forced to hold it until I couldn't anymore, so I was constantly wetting my diapers, leading to repeated spankings and diaper changes. I was also sucking my thumb a lot just to cope during those moments, so to "help" they would stick a pacifier in my mouth during my changes. After a few days, I realized what they were doing, so I gave up asking to go pee and just started wetting my diapers the second I felt the need.
Turns out, this was a mistake, cause after a couple of weeks, the caretakers said that I apparently didn't WANT to be potty trained, so they decided that if I wanted to use my diapers like a baby, then I would be treated like a baby. So I was then moved from the toddlers area and into the nursery. First, I was made to dress like a baby, meaning I was either wearing onesies sized for kids, or clothes with crotch snaps for "easy diaper changes." Second, ALL of my bathroom privileges were removed. So, not only was I wetting my diapers, but I was also now messing my diapers, with the only positive being I wasn't getting spanked for using them since "Since you're a baby, using your diapers is expected." Lastly, since I was now a baby, I was given the full baby treatment, meaning when it was lunch time, I was fed formula from a baby bottle and made to eat baby food by the nursery caretakers, and when it was nap time for the babies, I was put into a crib and told to nap, otherwise I would get a spanking for acting up.
This went on for the rest of the Summer, after which, things went back to normal. After that, I would never take another diaper from the nursery. While I would describe the whole experience as completely humiliating, I had to admit that, while I was in the nursery, I had actually enjoyed getting treated like a baby, as when I was behaving, I was treated nicely and given the same amount of care and attention as any other baby in the nursery. I liked the comfort of snuggling up in a crib for nap time, the calming effect of sucking on my pacifier, and even enjoyed having my diapers changed by the caretakers. I was enjoying it so much, that I would sometimes let my mind go, and start acting like a baby. After I hit 10, I was allowed to stay home by myself during the summer, so I would take any chance I could get while home by myself to "play baby."