Who is this running kid wearing a shirt with Uchiha symbol? There's a kid wearing a shirt with Uchiha symbol, but I have no idea who s/he is.



Who is this kid?
After doing some digging around, I discovered this scene is from the episode The Night of the Tragedy. According to the wiki, this is simply just an animation error

Trivia
In one scene, there is an animation error that an Academy student is shown having an Uchiha crest on the back of his shirt, despite that scene happening after the incident.

We know for a fact that there are very few Uchiha remaining. While it is plausible, as @Hostile Amigo mentioned, that not every Uchiha was present during the incident, this episode is part of the Kakashi: Shadow of the ANBU Black Ops filler arc and shouldn't be counted towards canon.