Before I begin this story, I am going to give you a handy guide to the ages of the characters. Here I go from oldest to youngest.
Teddy Remus Lupin: 24
Victoire Apolline Weasley: 23
Dominique Ann Weasley: 19
James Sirius Potter: 17
Fred Lee Weasley: 17
Louis Arthur Weasley: 17
Rose Granger Weasley: 16
Albus Severus Potter: 16
Scorpius Hyperion Malfoy: 16
Roxanne Angelina Weasley: 14
Lily Luna Potter: 14
Hugo Granger Weasley: 14
Molly Audrey Weasley: 12
Lucy Daisy Weasley: 8
Phew! Well I hope that comes in handy. Now let's start the story! Also, this somewhat disregards the Cursed Child.
It was the summer before James had to start his life as an adult, so he was being especially immature. All the Weasley cousins and Scorpius were at the Grimmauld Place as they often were. When Harry and Ginny got married they cleaned the place up and moved in. Usually everybody hung out at the Burrow, but when the adults wanted to spend time together the kids always flooed to The Potter's.
"Guys!" James said "I got bored and decided to explore the attic, and look at this weird necklace!"
"James! Be careful with that! It is a time turner!" Rose exclaimed. "If you break it we could be sent anywhere in time and never get back!"
But Rose's yelling had startled James, and he dropped the time turner, and everybody disappeared.
Sorry it is so short, but I wanted to leave it on a suspenseful note.