How do you make a possessed Jack-o-Lantern cute?

[MonkeySage]

I want this character to be as endearing to the player as possible; he's basically a possessed Jack-o-Lantern with the personality of an 8 year old human child.

This is because he is pretty much an 8 year old child; he and his brother were in a pretty bad car accident, and he survived unscathed, but his older brother was in critical condition; near death with no ambulance in sight. A demon happened to be nearby when this happened, and offered to save his brother in exchange for the usual price, and the boy paid without hesitation. His brother's life was saved, but the boy's soul was trapped in a nearby pumpkin. He doesn't remember anything other than the fact that he has a brother, and he's looking for someone to fill that role. The player is intended to be a kind of surrogate brother for "Jack".

I want to make him as cute as possible, in order to endear to the player. Given that in terms of appearances, he's probably not that cute, I want to make up for it with character traits and personality.

[Estralita]

Perhaps like this?

[MonkeySage]

Possible, though I was mainly asking about personality suggestions. ^_^

[Erit]

Not sure how to help with "cute", but before you go there you'll want to make sure the kid isn't an annoying little tit, and to that end I'd suggest watching the Jimquisition episode "Think Of The Children!" for your crash-course on how to make child characters sympathetic and interesting. I forget the source for the words of wisdom, but "writing good children goes smoother if you think of them as tiny adults with a lot less life experience".

Make the kid at least want to be helpful and not burdensome, and don't make him whine too much within the guidelines of reason. Have him listen to the character(s) and be reasonably intelligent about things, give him a moral compass and a conscience. If he ever comes across as an entitled brat outside of a comedic circumstance, you have gone astray.

I believe another helpful example would be Alphonse Elric, especially given the backstory you've given us. Just make him competent and somewhat mature if naive, perhaps have him act a little clingy or saddened at the prospect of loneliness. I imagine that, as a pumpkin, he lacks much for self-locomotion, so perhaps a phobia of being left alone exists or could be developed over time. If he gets upset, either make it a decent reason or have him apologize for it later (going back to having a bit of maturity; part of maturity is being willing to admit when you dun goofed.)

If you make him sympathetic and likable, then he'll make himself endearing by virtue of being a sympathetic and likable kid.