I know with most AB/DLs there ABDLism isn't caused by abuse at all but with me I think that the abuse I went through as a kid is a major driving factor for my little side.
I pretty much went through abuse and bullying most of my life, ranging from getting black mailed which I haven't ever told a soul about, to small things such as being physically hit and abused, most of my abuse was verbal but that still causes damage.
Because of that I never kind of had a good childhood, not a single soul knows to what extent the bullying went on, but I do and being little is somewhat me experiencing what I couldn't as a kid.
Brings me back to the mindset of being a child, but without all the bad things that happened to me.
At the same time I feel like it's always been a part of me too, as I had interests in diapers most of my life, but I think puberty was a major driving factor for it, as I was bullied and found it a way to escape my problems diapers would just bring me into a happy mental state, without a worry.
That being said I can't remember most of my child hood, due to the mental blocks, but I can recall most of the abuse throughout high school, the betrayal even. It hurts me to this day.
I somewhat don't think I ever matured mentally, as I never was a child, I'm sure some little's can relate to that. I've known some adults who I suspect were little's (mostly a bit too childish like us :P) that had some messed up things happen to them.
A reason why I think I'm also mentally undeveloped is I still have the imagination of a five year old, me flying around or flying cars, silly little things.
I kind of never grew up sadly.