There are many things to love about Aang in Avatar: The Last Airbender. But, as we learn in the sequel series, The Legend of Korra, his parenting skills are not one of them. The latter made some big changes when it came to the character roster, mostly in expanding the age range. Where Avatar is focused on pre-teens and teenagers, its successor has large roles for adult characters, such as Tenzin, Varrick and Lin Beifong.
Their presence not only allows for incredible feats of bending, but also a diversity of experience and opinion. Tenzin offering himself as support to Korra throughout the series created a much different show than Avatar, and the breadth of opinion that characters of different age ranges could provide forced Korra and other characters to reconsider their own opinions. All major villains in Legend of Korra are also adults, so having people like Tenzin and Lin on her side helps tip the scales, whether through perspective or fighting skills.
However, these adults do not exist in The Legend of Korra simply to back her up. They have their own stories to tell and ways to develop that ultimately make the show stronger. The dynamics between characters becomes more interesting than simply kids interacting with other kids, and the more developed these characters are, the deeper their relationships can become. One way The Legend of Korra chooses to develop some of its adult cast is by using the oldest trick in the book -- daddy issues.
Aang's parenting style has come under a bit of fire ever since The Legend of Korra revealed he spent much of his time with Zuko and Sokka building Republic City, while Katara stayed in the Southern Water Tribe raising the children. However, it wasn't until Season 2 that Aang's children had the chance to voice an opinion. Aang's kids fall into a classic pattern of inferiority complexes that are simply exaggerated by bending. Bumi, as the oldest and non-bender, is overshadowed by Kya and her waterbending, and the two of them are nearly eclipsed by Tenzin as the first new airbender in a hundred years.
Throughout Season 2, the ugly feelings the siblings have about their upbringing come to light. While Tenzin himself had been oblivious to his siblings' jealousy, the fact that Aang had treated Tenzin with special trips and treatment due to his airbending had not been lost on Bumi and Kya even as children. Tenzin is rather quick to point out that he has more responsibilities as the sole heir to Aang's airbending, which sets off a whole new argument as Kya was the only one to move to the Southern Water Tribe to be with Katara following their father's death. It is painful for all three because their father is not there to confront. They only have their own memories and each other to try to deal with the way they were raised.
Parenting, and the result of it, is an incredibly heavy topic -- particularly when the subject is how parenting went wrong. Even though the three siblings ultimately come to an armistice on agreeing it was not all bad, audiences of many ages are able to connect to problems with parents. Seeing three adults being petty and jealous makes them more relatable to younger audiences, and simply makes them relatable to older viewers. The Legend of Korra could have made the decision to make Aang the best father ever who treated all his children equally, but instead he was made into a real person, flawed and capable of making mistakes that ended up really hurting his kids.
In fact, this will also apply to Toph and many others in The Legend of Korra, who hurt the ones they love whether or not it is intentional. Bumi, Kya and Tenzin are hurting each other and hurting from the way they were raised, and the fact that they express such a complex emotion makes them intensely relatable, both for their flaws and actions. With this complexity, they add more to the story simply by existing in it, but also through the interactions they have with others and understanding more about how they view the world. For example, when Tenzin is unable to enter the Spirit World and Jinora is, Kya knows her little brother enough to be able to comfort him, because Tenzin simply isn't used to things not going his way and it's his turn to feel a little jealous.
In a show where romantic drama often ends up breaking hearts, the family drama of Aang's children is a grounding force, something most audiences can relate to, and the payback for exploring the siblings' dynamic ends up improving The Legend of Korra. The bonds between them matter more and they likely matter more as individual characters. Korra's own dynamic with Tenzin becomes deeper with Tenzin's new understanding of what his childhood really was like and the reminder that Tenzin is a result of imperfect parenting -- the same way Korra is a result of her own troubles.
Bumi and Kya are both able to contribute more to the show going into Season 3 as well, due to the way they were able to lash out at each other and ultimately mend some broken bonds. It may not be fun to face that Aang was a bad father, and perhaps all his children would have been better off, but this bold choice from the show-runners definitely improved The Legend of Korra.