Little Pieces
Katara could see little pieces of Zuko in her children. And not just golden eyes or alabaster skin or straight dark-as-ink hair. She saw Zuko in the way of their determination and perseverance. If they messed up they would get back up and try again. Sometimes they were awkward and hesitant, and they talked to turtleducks. They were very concerned with what was right- and she always rolled her eyes at how often they used the word 'honor'. But they were brave and outspoken, and maybe that was a little bit of her as well.
Hikaru, their firstborn, while not a bender he still held immense fighting skill with swords. Not only had Zuko trained him, but his Uncle Sokka did as well. Hikaru was a tactical genius, even at just 16. He was mature for his age- always so serious. (Definitely Zuko's son- practically a clone.) He could be a bit blunt, but he had all the great qualities of a leader. Katara knew he would make an amazing Fire Lord, just like his father.
Kya was probably the least like Zuko. She was the spitting image of her mother, and had even inherited her water bending. She was kind and gentle-tempered (where she got that from Katara wasn't quite sure. Her and Zuko were both hot-headed. Probably Iroh's influence). The most Zuko-thing about her was how awkward she could get. Jokes that didn't land, painfully awkward silences, and muttering to herself. Or maybe that was all because she was 13. Either way, it was pretty adorable. Katara planned to give her Gran Gran's necklace on her birthday next year.
The twins, Zuri and Kai, seemed to be a perfect mesh of their parents. Zuri was slightly paler, with golden eyes but soft features and a mess of curly brown hair. Kai was mocha-skinned and blue-eyed, but had the distinguishing sharp features of the Fire Nation. They were both fire-benders, but at the age of nine they didn't have much mastery of it yet. Zuko was always excited to train them. (Their Uncle Aang always showed them dangerous tricks and got berated by Zuko.)
Katara loved to watch them grow and become their own people with their own ideals- but she would always cherish seeing those little pieces.