Sherlock is pregnant with twins. Weird cravings sends John out on a four hour errand to pick everything up for his pregnant Omega.
Harry Potter is the younger twin of the 'Boy-Who-Lived' Ethan Potter. But who cares about little Harry? Not his parents. Not when they have their precious boy. The Wizarding World forgets about him. Dumbledore informs the Potters of the wrong child and how would the rectify their mistake when the come to realise.
Harry is given to the founders until he turns eleven.