The Mini Fairies are an extension of Tooth herself. They first appeared when she was caged by the Hunter. In the books, she can communicate with them via telepathy.
In the movie, they don't speak as they just chirp but Tooth can understand what they are saying. They are also infatuated with Jack as Tooth has a slight crush on him too. She's a bit jealous of them, because they can act unrestrained and bat their eyelashes at Jack, while she has to be more reserved. Instead, she tells them all to calm down and behave more seriously. 
Jack: [confused] My - my what?
Tooth and Jack share a good relationship. Tooth is really sweet albeit a little clumsy around Jack. She has a crush on Jack; while she is more reserved about it, her minions - as they're extensions of herself, they feel mostly the way she feels - are more obvious about their crush, what with their fainting and fan-screaming. Tooth has to constantly calm them down due to their obvious behavior. She was the most excited one - not to mention a little dreamy - when she learned that Jack Frost was to be made a new Guardian. As soon as she met Jack, she firstly checked his teeth, the main reason for her crush at the time. However, as her crush continued throughout the movie, it likely developed more based on Jack's personality rather than just his perfect teeth after she got to know him as a person.They had a proper conversation after the Tooth Palace was attacked. Jack's more considerate side surfaced as he talked to her, worried about her well-being. She was the first one to know that Jack was unaware of his past, when she told him the teeth stored memories, and that she had his teeth too. Jack then realized that he was the only one apparently without any memories of his past. Tooth was stunned as she genuinely did not know about his memory problems and showed remorse throughout the film as she could've helped him had she known. The two work together collecting the teeth and Jack is amused but slightly confused by her extreme enthusiasm for the job. She later collects Jamie Bennett's tooth personally with him and after realizing he knocked it out himself, gently chides Jack for doing so. Working with Jack to collect the teeth and seeing Jamie up close reminds her of what she always loved about her job the most: seeing the children. Jack tells her that its different to work with the children up close rather than from a distance as Tooth and all the other Guardians do and Tooth wonders why she ever stopped going out into the field. When she expresses regret over his memory problems, Jack puts that aside telling her that they'll help her first then deal with Pitch. During the skirmish with Pitch, Tooth saves Jack from a fall after he defeats Pitch and is impressed by the power he displayed though both are confused as Jack didn't know he could do what he did. Despite the close friendship they develop, Tooth instantly thinks bad of Jack when he has his Tooth Box and Baby Tooth is missing though she seems more horrified than angry at his apparent betrayal unlike Bunnymund and North. She makes no move to stop Jack when he leaves and along with the others, turns her back on him. However, when the Guardians travel to Jamie's house as he's the last believer in the world, she's excited to see Jack there. However, when Jack catches her from falling out of the sleigh, she's left embarrassed to be falling in front of him. Unlike North and Bunnymund, Tooth expresses no suspicion over Jack's sudden return and saves him during the battle with Pitch to his gratitude. When Jack is offered the chance to be sworn in as a Guardian once more, Tooth anxiously watches and hugs Jack as soon as its over. While she's embarrassed by this, Jack enjoys it but they are broken up by Baby Tooth.
Jack is more careful and caring when he is interacting with Tooth, losing his care-free demeanor around her, possibly because she is the female of the group. On the other hand, Tooth is more conscious around him, presumably due to her crush, but is still helpful. She ends up finding a close friend in Jack and a confidant.
North: We will collect the teeth!
North: We collect teeth, children keep believing in you!
Tooth: We are talking about seven continents, millions of kids --
North: Give me break. You know how many toys I deliver in one night?
In the movie, their interactions aren't much, though, it can be said that both share a father-daughter relationship. After Tooth started shedding her feathers, and her Palace was starting to disintegrate, North was the first one to step up and provide her support by thinking to collect the teeth. This was due to his concern for her, and his duty as a leader. After collecting the teeth, he asked her how she felt out of concern, and she replied, "Believed in!" All these little things show their concern and love for each other as a team, and as friends,. It is also seen that North has a nickname for her, and it is "Toothy".
Tooth: [after Sandy is back] Oh, Sandy. You're all right!
Not much is clear about what level their relation stands. Both share an understanding about their work. While North and Bunnymund were having their usual argument over Christmas and Easter, she said, "Sorry, not all of us get to work one night a year. Am I right, Sandy?" However, she was completely oblivious to the fact that Sandy was trying to get her attention and not agreeing with her question due to the fact that she instantly went back to work. At Sandy's supposed death Tooth's sadness and at his arrival Tooth's happiness showed that she had a good relation with him.