I wanted to practice drawing young character proportions + a different style of diaper, so I found a picture of Tommy Pickles from Rugrats and copied it. Of course, I changed it a bit for practice, and I personally think it turned out better.

One thing to take away from this: you don't need a lot of detailed lines to make a diaper look thick. The most important lines are around the legs though. You'll still need to add those, but you don't need to make the overlapping very complex. Just enough to convey the feeling.

(And in case you were wondering, I didn't grow up watching Rugrats. I think I saw part of the 1st movie once, but that was about it.)