So often do we ignore the shopkeeper that sells us our goods, the roguish stranger we pay for information, our sisters and brothers. Let's talk about them.
When coming up with family members, you have only a few options. You don't want to come up with too many, because there will far too much conflict. You have to give your characters time to grow accustomed to that family member being there for them. The support our family offers us, there's a reason we complain about not knowing what we have until it's gone. Not until you have established an emotional connection can you sever it, and take from them what they took for granted. The helpful mother, the loving sister, or the boyishly charming brother can all tug at these heartstrings simply by disappearing from your characters' lives.
Weaponsmiths, armorsmiths, apothecaries, blades for hire. No matter the good or service, someone has to sell it to you. Unless for story reasons, your merchants must be good at what they do. Make sure they try to rip your characters off from time to time. Not every shopkeeper has a heart of gold, and most of them only want to take yours from you, and sell it back at a mark-up.
Kids are tough, cruel, and annoying. They don't have the sense of morality that comes with worldly experience, so they rely, naturally, on an "eye for an eye" mentality. If one punches another, nothing in the world matters until the blow is returned.
Not all kids are horrible, however; Their mentality comes in as many flavors as ice cream. Reality, for them, is simultaneously monochrome and technicolor. Not all children are innocent, either. The signs of psychopathy can be found early in mental development.
The hardest thing about emulating children in our stories, though, is the fact that they universally possess a sense of whimsy we adults have long-since discarded for fear of being thought maniacal.
It's a double-standard, but that's how society works. We can't always have our heads in the clouds like they can. Life gets in the way of that.