Other mistake: Before the battle, the leader of the waterbenders says that he will have everyone extinguish as many sources of fire as possible. When the firebenders come up from the ground at the start of the battle, all of the torches lighting the city are lit.
Trivia: Gran Gran tells Katara and Sokka about her old friend Hamma, one of the last waterbenders rounded up by the Fire Nation. In the original series, Hamma is the Southern Tribe Waterbender that teaches Katara bloodbending in Book 3.
Trivia: Noah Ringer, the kid that plays Aang, was a martial arts State Champion in his home of Texas. To keep cool in the dojo, he shaved his head, and later painted a blue arrow on his head when his friends commented that he looked like Aang.