For me it's all about the wetting. I'm a little, not a baby, and I'm usually but not always around 9-12.
Now I can just simply enjoy wetting my pants for fun, and not be in little mode. Sometimes the opportunity arises, like I'm about to do a load of laundry, and I'll just simply pee my pants before adding them to the load. I won't indulge in any pleasuring activities, but will just use the chance to wet myself.
The same with diapers. I don't necessarily have to use them to enjoy them. Sometimes it's just nice and comforting, and gives me a feeling of safety and security to just have one on.
But while I can enjoy these things without being little, I can't be little without wetting. That's what being little is to me, having an accident or just choosing to wet. That's why I'll wet myself nearly every day, even if it's just my underwear before I have a shower, because I enjoy the wetting but don't have to be little to do so.
But if I have the time and privacy, then little me comes out. I'll dress in my little clothes or diaper, and spend some time mentally regressing to whatever my preferred age at the time may be, and I'll wet myself along the way. If I can't get wet, I can't be little.
I know others can play with toys or watch cartoons for hours and just enjoy it, but while I can get a kick out of it, it's just a prelude or distraction until the main event occurs and little me wets himself. I don't get a huge amount of chances to do this, but try to at least once a week.
I'm not trying to self promote a thread here, but only last Saturday I had the house to myself all day and night, and managed to spend all afternoon and evening in my diapered little mode. It was the longest I have ever spent little, and I loved it.
Only yesterday I made a long blog post about it on this site if anyone cares to read it.