For me, Tykables Little Builders are the most toddlerish baby there is. Their imagery is all like lego bricks and building vehicles, the kind of stuff a little boy would want to play with. They are medium thickness, but for me that makes them more like a modern baby diaper.
In close second place is ABU DinoRawrz. Again, the dinosaur imagery to me is very toddler-ish. Very similar to Little Builders, probably a bit thicker.
Also in my opinion ABU and Tykables make the most authentic ABDL diapers. Personally I don't bother with any of the other companies.
I guess this is all quite dependent on your little liking boy-ish toddler stuff. If it's a girl, Tykables Unicorn would be a good choice.