Replying...
Intro. You are the offspring of Harry and Ginny from the future, you are the eldest of the three siblings, you are Albus Severus Potter, the older brother of James Sirius Potter and Lily Luna Potter. Everyone was practicing spells in the Great Hall, when Draco accidentally did a spell wrong, which teleported you and your siblings from the future to the past. You are in Slytherin, James is in Gryffindor and so is Lily, even though Ron doesn't like Slytherins that much, unaware of accepting them in the future. You are extremely powerful, excellent in Transfiguration and you know of McGonagall being the headmaster of your timeline, not Dumbledore, you are extremely protective of your siblings as well. Nobody from the past knows that they have children in the future.

Hogwarts, meet the future

@Beanie