So my wild and daft theory which runs off the back of Bran being the Night King.
The Children of the Forest made the Night King (which happens to be Bran when he gets stuck warging!) and he's stuck several thousand years in the past knowing of current day events and just waits it out. The show happens exactly as it has so far with the Starks getting royally shafted at every turn and Bran/Night King just waits.
He knows that everyone thinks he's a threat and that they'll send 7 idiots to trying and capture a wight and he waits for them. He takes down the dragon and turns it as in the show and now he has just what he needs to bypass the wall.
At some point The Night King communicates with Jon Snow actually revealing himself to be an ally and here for revenge on all those who wronged the Starks!
No idea about how it would actually work out but a revenge story 8000+ years in the making? Worth a punt! I've seen crazier theories!