If you're still taking prompts: Uncle Sokka! I haven't read a single thing about Sokka and his niece and nephews!
“Oh, sure, Katara, I’ll watch the kids for you,” Sokka grumbled to himself as he picked up the food Tenzin had blown out of his hands. “How hard can it be?” He gathered the rest of the rice into the bowl and stood up, raising an eyebrow at a giggling Tenzin. “No. More. Airbending,” Sokka told him as he pointed at the one year old.
Tenzin slapped his tiny hands on his high chair and squealed with laughter as he blew another gust of air in Sokka’s face.
“Uncle Sokka! Uncle Sokka!” Bumi shouted as he ran into the kitchen. “Come outside, we gotta show you something!”
Sokka picked Tenzin up from the high chair, groaning as he wiped drool from his nephew’s mouth. “What is it?” Sokka asked as they walked outside. He set Tenzin down on the steps with an Acolyte and followed his eleven year old nephew towards the greenhouse.
“Show him, Kya!” Bumi exclaimed.
Out of the corner of his eye Sokka saw a small figure rushing towards him with their arms held over their head. Before he could do anything, his niece spattered mud all over the place, and the four year old burst into laughter.
“I’m a mudbender!” Kya cheered, covered head to toe in mud.
Sokka wiped mud off his face, and Bumi roared with laughter as his sister started bending mud balls at him.
“Uh, Councilman Sokka!” the Acolyte called from the steps. She was holding Tenzin an arm’s length away and he was blowing air in her face repeatedly. “Help!”
Sokka smacked his forehead and groaned. He looked between his niece and nephews and suddenly felt a wave of admiration come over him for his sister. This was madness.
“Attack!” Bumi shouted. He and Kya pelted Sokka with mud balls and tackled him to the ground. “Surrender, Sokka of the Southern Watertribe!” Bumi commanded. “You’ve been defeated!”
Sokka closed his eyes and laid silent in the mud, and Kya climbed onto her uncle’s stomach.
“Are you okay, Uncle Sokka?” she asked.
“Sneak attack!” Sokka shouted as he grabbed Kya. He hoisted her over his shoulder as she squealed with laughter and started chasing Bumi through the mud.
The Acolyte watched in concern and tried her best to keep Tenzin in her arms. “Councilman, I don’t know how Master Katara would feel about-!”
Sokka turned to look at the Acolyte with a huge grin and mud dripping down his face. “Forget Master Katara!” he told her. “I’m in charge now!”
“YEAH!” Bumi shouted. “Forget Mom!”
Sokka went over and took Tenzin from the Acolyte and laughed as he blew the mud off of his face. He noted the Acolyte’s look of disapproval and he raised an eyebrow. “What?” he questioned. “If you can’t fight ‘em, join ‘em!”