Soon after the war ended, Andromeda went into depression, having lost her husband, her daughter and her son in all all at once. She found herself unable to take care of baby Teddy Lupin, who reminded her of Nymphadora increasingly more each day. Young Harry found himself taking the responsibility at an age where he himself needed help to get over the events of the previous years, but he rose up to the task marvelously, aided fully by the Weasleys and Hermione, of course.
After Harry got a job and got a small house in Godric's Hollow, he took Teddy to live with him full time, aiming to connect to the young boy and guiding him through life, as he knew Sirius would have guided him if he had the chance. Then he married Ginny and even before they had James, their family had seemed complete.
When Teddy reached the age of six, Harry and Ginny realised that it was time that Teddy learnt about his parents and his true identity. They sat him down one evening after tea and explained to him everything about Voldemort and the Marauders and Remus Lupin and Nymphadora Tonks, making it as simple and as easy as possible for him to understand and process all this information.
Teddy was heartbroken. He couldn't believe that Harry and Ginny weren't his parents, let alone that he had never even gotten to known them. For days he couldn't bring himself to look at Harry or Ginny or any of the Weasleys the same way, and the only person he ever wanted to talk to was Andromeda, who would tell him stories about his mother, and he would come back from the trips feeling much better about everything than before.
When it was finally time for young Teddy to go to Hogwarts, he wished more than anything that Andromeda could accompany him to platform 9 and 3/4, but her increasingly dwindling health had caused her to get bedridden. When the Hogwarts express finally reached Hogwarts, Teddy felt overwhelmed with feelings, realising that this is the place where his parents had died. He stepped into the Great Hall and stood frozen to the spot, soaking in whatever he could about his parents. This is where they'd spent their last moments, defending this place and its people from the onslaught of Voldemort.
As Teddy sat gingerly on the stool under the tattered Sorting Hat, he couldn't care less about which house he would go to, thinking only of how much he wanted to avenge their deaths. When the hat announced that he Teddy Lupin had been sorted into Ravenclaw, he moved towards the cheering table with a heavy feeling in his chest: There was no one who would hug him and pat him on the back and tell him that they were proud of him for making it to Ravenclaw.
Teddy quickly started showing talent in Herbology and Defense against the Dark Arts, and turned out to be an absolute disaster at potions. Teddy knew to forgive Harry and the rest when he went to the staff room to see Professor McGonagall and heard her telling the rest of the teachers how much Teddy Lupin reminded her of both his parents, and how the Potters and the Weasleys had perfectly raised Teddy to make him more like his parents than them.
Teddy, who had been rebelliously sporting a pink head of hair, promptly changed his hair colour to black, and switched back between black and red to pay respects to the two people who would, as far as he was concerned, always be his parents.