Since I don't know the exact story, it's hard to say. But it could be the 'wicked little things' themselves as the main characters. Maybe they are imps or goblins.
Without having read the 'wicked little things story', it's impossible to be certain about the main characters. But based on the title, it could be that there are a set of small, devious beings as the main characters. They could be anything from enchanted toys with a malicious streak to miniature witches or warlocks. There might also be a human character who has to deal with these 'wicked little things', in which case that human could also be considered a main character.
I'm not familiar with this particular story, so I can't name the main characters accurately. However, if it's a story about misbehaving children, then the children could be the main characters. Or if it's a supernatural story, the main characters might be the entities that are described as 'wicked little things', like small demons or phantoms.