The Avatar's wife's first child is a firebender.
(They had known, obviously.
"I can't stand it, I am so hot," Katara had whined, constantly, throughout the pregnancy. "Is this how you feel all the time?" she'd asked Zuko, frowning at him, like it was his fault. (It was.)
"I'm sorry," he'd said, though he hadn't looked sorry at all. Aang had blown a breeze around her, and Zuko had softly removed her clothes, and it had helped a little, until both men's bodies had surrounded her and made her even hotter. But it didn't seem to matter as much in that kind of situation.)
They pass it off as some fluke of the Avatar powers. Nobody's really fooled, probably, especially since everyone can see the way the Fire Lord looks at the Avatar's wife. But Aang has been steadfast, honest and true throughout his life - the public one, anyway - and if he wants to spend all of that honesty capital on this one, huge lie, so be it.
The Avatar's wife's second child is a waterbender.
(Aang had tried his best to look like he didn't care, as soon as they had realized that Katara was pregnant again. He would ask if she felt hot, then backtrack and ask if she was hungry, or needed anything, or if her life was the pinnacle of joy it should be. Zuko and Katara had smirked at each other every time.
"I'm kind of cold, actually," she had said, sometime in her second trimester.
"Hmm," had said Zuko, pretending to think about it. "Like there's a kind of breeze around you?"
"Possibly inside of me, even," she'd replied, her eyes exaggeratedly open. "What could it mean?"
"I hate you both," had said Aang. He had still gotten her a blanket.)
Suki's second child turns out to be a waterbender, too. Sokka explodes with pride as the two cousin toddlers bend their first drops at the same time, on one of the too rare occasions they're all together. He prattles on and on about water beating all of the other elements. Zuko looks at Suki, and she's rolling her eyes. He smiles. Neither of them point out their firstborn's abilities. (Toph is not as nice about hers.)
The Avatar's wife's third child is, finally, definitely the Avatar's child.
(Something had woken Zuko up in the middle of the night. His hand had reached automatically for Katara, softly going around her belly in a protective gesture like it did whenever his restless sleep was interrupted. He had stopped his movement, though, when he had listened a little more closely.
"It's not that I mind, you know," Aang had been saying. Zuko had looked up at Katara, trying to find who Aang was talking to, but her eyes had been closed, her breathing even. Zuko looked down, then, and found Aang's head resting near their unborn child. "I love Bumi and Kya just as much as I would if they'd been airbenders. Obviously. I'm not a monster." Zuko had felt his heart tighten and he had wanted to reach for his lover, to comfort him.
"It's just that... that it's only me. The Last Airbender," he had said, in a disparaging grandiose voice. Zuko had held his breath. "It'd be cool to have a buddy."
Zuko hadn't been able to stop himself anymore, and his hand had reached for Aang's, both of them tangling on top of Katara's round stomach. "I love you," Zuko had said. I wish you weren't alone. I'm so sorry.
"I love you too," Aang had replied. He had moved carefully, trying not to disturb Katara, and then he had landed in Zuko's arms and had stopped being careful. Zuko had done his best to make him forget, and forgive the sins of firelords past.)
The Avatar's wife's fourth, and fifth, and sixth child-
("It's too bad that Toph and Suki are ladies," had said Aang, as an thousandth discussion of a possible fourth child was starting again. "We could probably get one of them to impregnate you otherwise. Keep that Avatar's children myth going."
"Because you wouldn't mind me having sex with either of them if they'd had male genitals?" had asked Katara, an eyebrow raised.
Aang had shrugged. Zuko had frowned.
"The more the merrier, is that it?" asked Katara again, smiling disbelievingly at her husband. He had smiled back. Zuko had growled. "I know the Avatar loves the entire world, but this is above and beyond-"
"I'm just going to stop this train of thought before any of you get ideas," had said Zuko, alarmed, possessively wrapping an arm around each of them.
"I don't want a fourth baby," had said Katara, smiling between Zuko's annoyed, worried kisses.
"It wouldn't have to be an earthbender," had said Aang. He had gotten interested in the proceedings, sneaking a hand into Katara's dress, but hadn't stopped talking. "Another airbender would be great, I mean, what if Tenzin doesn't want kids-"
"I don't want a fourth baby," Katara had repeated, and Zuko had started kissing Aang, too, trying to shut him up, because he had heard both sides of this dialogue a hundred times.)
There is no fourth, or fifth, or sixth child.
(The Avatar's wife's first grandchild is an airbender.)