Baby Zuko firebending for the first time:
I like the idea that Uncle Iroh was the first person to get Zuko to firebend. Ozai wanted nothing to do with raising a child Especially one he thought was a non- bender.
Ursa loved Zuko and spent most of her time with him. She had no way of training him to firebend in order to please Ozai. So she spent as much time with her baby as possible just in case Ozai actually decided to throw him out of the royal family.
Iroh comes back from a small war mission, and decides to visit with his brother's family. One night while Ozai was out practicing in the courtyard Iroh companies Ursa and Zuko playing in the living room.
Iroh noticing Ursa's general destress asks how being a new parent was going. Quietly she says " he's not a bender...the sages have tried everything." Iroh a little wide eyed knowing the seriousness of her statement. "Well those old timers don't know the first thing about making a baby laugh."
Iroh already lowering himself down to floor where baby Zuko was, while Ursa looked confused. Iroh looking up to her after having scooped the little bundle onto his lap. "Firebending comes from the breathe my dear. The best way to check to see if a baby is a firebender is to see the spark in his eyes."
Ursa a bit triggered by his statement since Ozai specifically pointed the lack of spark in Zuko's eyes the day he was born. Iroh taking note continues "the best way to get that sparkle into a baby's eyes is to get them to giggle" wiggling Zuko around tickling him "isn't that right little one." Nothing.
Iroh loved babies, and had an gift for making babies smile and giggle. But his nephew seemed to have his father's sense of humor... very little.
"...hmm let's try something a bit different" Iroh shifts to grab his tea cup from the table. Drinking a bit, Iroh lets out a small fire breathe and holds back to make smoke come out his ears.
Zuko starts to giggle so much he gets the hiccups. Making little flames shoot out of his mouth. Much to Ursa and Iroh's delight and amusement.