One prevalent fandom "headcanon" that continuously ticks me off...
It's the one where Katara and Aang start growing nervous or are somehow upset and/or disappointed that the first two kids they have aren't airbenders, and that they are only happy and satisfied and relieved when Tenzin is born and found to be an airbender.
Those two would be like any parents and just be INCREDIBLY PROUD THAT THEY MADE SOMETHING. Airbender, waterbender, non-bender, these are their CHILDREN, and I'm pretty sure that both of them would value that over nationalities and genetics.
So, recap:
No disappointment.
No angst and self-loathing.
No "let's try again" attitudes.
And ABSOLUTELY NO shunning the children because they didn't deliver.
They're Aang and Katara, not Ozai. They're proud of their children, no matter what they can do.