Basically you have to win as the neighbor while the basement door is open.
The best way to accomplish this is to use bagger/neighbor then capture all kids except for 1, use the crows to find 3 keys and wait until there is 3 locks remaining on the basement door matching the keys you have.
(Tips: 3 keys just to be safe although 2 should be enough. You might have to open some locks to help the last kid)
When you are ready knock out the last kid by throwing stuff at them, then run over to the basement door unlock all locks + make sure to open the basement door
then run back to the kid and capture him to win the game.
(Tips: you can also level up the default neighbor to unlock bear traps which you can place in front of the basement door)