After Harry has defeated Voldemort and led the defeat of the Death-eaters, it is natural for Harry to want R & R. Perhaps it is with this in mind that Rowling imagines him spending the rest of his life in blissfully wedded, child-spawning suburban retirement with Ginny Weasely; or maybe it's because Rowling has developed a perverse hatred for her famous character. Whatever. It's all bollocks.
First of all, in the aftermath of a war that has caused widespread death and chaos and that has destroyed the institutions of the Wizarding World, there is little time for rest and relaxation. Whether he wants this or not (hasn't that always been the case?) Harry stands as the de facto leader of Wizardly England. He immediately turns to the task of reestablishing and reorganizing the Ministry of Magic, with the assistance of Mr. Weasley and Kingsley. In doing this, Harry's policy is reconciliation. Harry remains Minister of Magic for five years, after which he retires from public life, passing his responsibilities to Kingsley.
Harry DOES have children, but not with Ginny. Although Ginny loves Harry, and they remain close friends always, she realizes that he has a very restless spirit, and that, even if he didn't have a restless spirit, Harry couldn't avoid spending the rest of his life as a target for every two-bit wizard with a reputation to make. The Famous Harry Potter cannot make himself unfamous even with the most powerful magic. Also, Harry is committed to remaining an undefeated wizard the rest of his life, because that way the Elder Wand can lose its power and Dumbledore's dangerous legacy can finally be put completely to rest, when Harry dies. Harry's life will be far from quiet, no matter what.
There is ONE who has fought at Harry's side from the beginning of his adventures, one whose strength and understanding he has relied on more than anyone else's, one who has loved him fiercely: Hermione. It is Hermione who joins with Harry in a lifelong partnership of love and work. But not right away.
After the defeat of the Death Eaters, Hogwarts lies in ruins, both figuratively and literally. Despite the death of Albus Dumbledore, her beloved, and the destruction of Hogwarts itself, her home, Minerva Mcgonagle stands ready to take over as Headmaster. But it is obvious to all that Hermione is destined to restore Hogwarts. Mcgonagle sends Hermione off to complete her education by studying wizarding and witchcraft around the world. For five years Hermione travels. She and Ron try to keep up a long distance relationship at first, but Ron, like Ginny, soon realizes that he longs for a domestic harmony that will never happen with Hermione. He ends up marrying Katie Bell, his old quidditch captain after her retirement from professional sports.
Harry too keeps in touch with Hermione and before long he finds that they are writing to each other almost every day. Hermione always has opinions about what is going on politically (especially in regards to Muggle-relations and Magical creatures) and Harry finds that he is no longer disinterested in Hermione's magical studies. He has become as eager to learn as Hermione herself. Slowly the emotional reticence between them slips away. When Hermione returns to England, she immediately joins the staff at Hogwarts, teaching Wizarding History. Soon after, Harry resigns from politics and also joins the staff at Hogwarts, teaching Defense Against the Dark Arts. Neville is there too, teaching both Herbology and Potions. Percy Weasely is overseeing the restoration and care of Hogwarts' buildings and other administrative tasks.
When Mcgonagle retires, Hermione becomes the Headmaster of Hogwarts.
Ron moves to Diagon Alley and with some financial help from Harry, he buys up most of Nocturn Alley and establishes a tavern/bed and breakfast, which Mrs. Weasley helps him run. George buys some property in Nocturn Alley too, for the reopening of his jokes and toys shop. He has a magical painting of Fred that keeps him on his toes and keeps the new ideas and inventions coming. Pretty soon Nocturn Alley is known informally as Weasel Alley!
After the harrowing events of Deathly Hallows, Ollivander realizes that he can no longer remain England's only wand-maker so as soon as he recovers he begins a search for a protoge. For many years this search is a fruitless one, the combination of disciplines and traits necessary in a wandmaker is a complex one. Eventually Teddy Lupin, who was raised by his grandmother Andromeda Tonks with help from honorary grandparents Molly and Arthur Weasley, Godfather Harry and numerous honorary aunts and uncles among the Order of the Phoenix-DA crew, shows a love for craft and for tree lore and a fascination with magical creatures that soon blossoms into a talent for wandmaking. His true and beloved home is the Lupin ancestral home on the Dartmoor, but he often travels in search of ancient forests and magical creatures both during his apprentice-ship with Ollivander and afterwards. With Ollivander's blessing he eventually opens a shop in Weasel Alley and whenever he is there, it becomes one of the most crowded places in the Wizarding World. He has more tales to tell than anyone since Gilderoy Lockheart, and his are usually true!
Luna Lovegood, by then a prominent Artist-Witch, is much older than Teddy, but she always hangs out at Teddy's wand shop whenever he is in town. Eventually, she and Teddy get married and she becomes his full-time collaborator. She claims that wands for witches have never been quite as well made as wands for wizards and makes a point of changing that.
Ginny becomes a teacher at Hogwarts too, teaching Muggle Studies. She and Neville get married. Percy ultimately goes back into government, in buildings and works.
Many adventures lie ahead for Harry Potter and his friends, as many as there are fan fiction writers to write them!