Writing a Spoiled Sweet hero

In Fafnir's Bane, the protagonist Sigurd is raised by a dwarf in a mountain forest. His adopted father gives him everything he wants, yet he still turns out to be a very nice person.

How should I handle this aspect? In particular, what makes a nice kid who happens to be a bit spoiled different from a brat?

Brats aren't nice. Spoiled isn't synonymous with brat. Just because a kid is given things, that doesn't mean they'll turn out to be bad people. It probably depends on if his parents taught him good morals or punished him when he got out of line.

A Spoiled Sweet character actually has a relationship with the parents. They talk to the child instead of giving presents because they can't be there physically. They express love to the child in words.

Buddah would be an example.

His foster father is the only other person he knows well and the only other person in their house- so they're very close.