The thing is, there will be outliers in all areas. Most people aren't supermodel material, but they do exist. A child at DS' old school was reading and comprehending Harry Potter when he arrived, at almost 5. He's staggeringly gifted (and, sadly, socially isolated in consequence). I've never known another child like him. But he was there. He's real.
My own DS can read and comprehend Harry Potter. He's on the Able, Gifted & Talented register not only for academic subjects, but for problem-solving ability, and general knowledge. But... there's a very substantial but. He is autistic. He has the extraordinary level of focus that strong special interests in a bright child can offer - that is one of the gifts autism can convey - and his obsession as a preschooler with phonics and lego and maths translated into real facility with numbers, and a love of stories that now means he loves to read so he can escape his reality. Because he does need that escape. He suffers chronic anxiety (common, in autism) and he knows he has difficulties knowing how to interpret the body language and words of others. He knows the world is confusing and he also knows he has far more sensitivity to touch, sound, taste and smell than anyone else, which makes the world a barrage of draining, and sometimes terrifying, sensations. His life is very hard. I am hopeful that his academic talents will go some way to compensating for that, and that he will be employable as a result, but he is at seriously elevated risk of mental health problems. All autistic people are, because we live in a world that has low tolerance for interpersonal diversity, and most autistic people cannot predict or understand the level of hostility or mockery they inevitably will encounter.
I understand that people don't like to think that some kids are just able to do this stuff. I understand that they want to think they don't understand what they read, or the parents are lying. And I am sure in some cases that is true. But surely the reality is that most of us, and most of our children, will be average, and that's okay. That's better than okay; that's lucky. I would swap my little boy's academic abilities for happiness and social ease in a fucking heartbeat, and parents who worry about their children tootling along cheerfully in the middle lane, because some kids are roaring ahead in the fast lane... well, just sometimes, remember that your kids aren't in the slow lane, either. I do, with mine, when I see what other parents with ASD kids handle, and I know I am lucky. But those of you who are luckier still, please try to remember, and appreciate it. Normal is great. Average is splendid. Rejoice in it.