How to get Harry and Fleur in touch before Hogwarts. Point of divergence: The Dursleys take Harry with them on a trip to France (much like the zoo trip, he's there but not involved, they could find no holiday caretaker for him). There's a traffic jam, the truck behind them doesn't brake in time and crushes the car. Harry survives due to accidental magic. Which alerts the French ministry. They take Harry with them to the nearest magical hospital (for the shock and formalities if nothing else).
There the healer assigned to Harry, a certain Appoline Delacour, ends up introducing Harry to magic and then realises who he is. Since there is no obvious guardian, she offers to take care of him until the formalities are sorted. She manages to make him open up a bit, and what she finds out disgusts her. Whoever was supposed to watch over him failed miserably. She reports this and the French end up denying all requests to send Harry back.
Meanwhile, you can go wild with adorable Harry&Fleur interactions (children trying to work around a language barrier, big sister Fleur)