If PP knew Henry was the boy he was after, why would he send him to Storybrooke? Why not kidnap him as a baby?
Maybe he had to be of a certain age? Ep 1 is called Heart of the Truest Believer, and if that does end up referring to Henry, well, babies don’t believe in anything. So maybe PP had to wait until such a time that that strength was sparked in Henry before he would become useful. If so, then the child had to be kept in a secure environment until such time, and SB was perfect for that. And that something that turned him into the “truest believer” was learning the story of his family and having to fight to prove the truth to Emma.
Which all cycles back to THO, controlled by PP, having controlled August’s actions in breaking up SF, because if they were a happy little family all living together, Henry wouldn’t have been put in that extreme situation he needed to be in to prove himself and become exactly the “true believer” that PP needed him to be.
Perhaps?