After Voldemort was defeated by Harry, Harry married Ginny and they had four children. They lived a happy, comfortable life.
One day, Harry had some sort of strange impulse, found the Deathly Hallows, and handed them to his fourth child. As a result, his children transmigrated in spectacular fashion.
James: "Oh my god, where are we? Is this Hogwarts? We've arrived in Dad's time!"
Lily: "Oh, Dad, come save us! James is going to tear this place apart! Oh my god, James, don't touch my parrot!"
Albus: "Harry, think of something, quick. This place is really scary."
Harry: "What can I do? Albus, please, act like a man and get off me!"
Harry is my fictional fourth child of Harry. I made one change to the Elder Wand from the original: it can be repaired.
There are only three Deathly Hallows, the wand in Dumbledore's hand, the Potter family's invisibility cloak and the Resurrection Stone, and the four children can't tell them apart at all.