Look. I'm biased.
So, here's the thing. I could write pages that explain my perceived logic of "cute", but the abridged version is composed of several key factors.
1. Trunks is a mischievous brat that helps exemplify Goten's adorable qualities as his opposite.
2. Goten has two basic modes. One is to be a Super Saiyan or Gotenks, while the rest is to be played for his "cutesy" factor. It is his function in the story to say and do things that invoke cuteness and basically make you want to coddle him in one way or the other, moreso than any other character. Even his voice is designed to reflect that (and that's regardless of which version you're watching). He's seven years old, so his inflections and emotions are exaggerated.
3. Long sleeves. Yeah, when you're short stuff and your sleeves are almost longer than your arms, it does something.
4. The strong-as-fuck-but-wouldn't-hurt-a-fly effect.
5. Abundant moments of hyper-cuteness like pictured in my avatar.