A Fan Theory by Samantha Lee - @SamsJag
In the Season 3 promo Mr. Gold says, "Neverland is a place where imagination runs wild." I believe this is a clue to the nature of magic in Neverland. I think that magic in Neverland is powered by imagination and imagination is strengthened by belief. Perhaps this is why Neverland is controlled by children; they still own their ability to believe in what their heart tells them instead of what their mind says is logical. This is why Henry is so important to Peter Pan.
Since the very beginning of Once Upon a Time, Henry's greatest strength has been his belief. He believed in the Curse. He believed that Emma was the Savior. He believed that David was Prince Charming. He believed that Emma and Mary Margaret could be rescued from the Enchanted Forest. Not only does Henry hold on to his belief, but he makes those around him believe too. He helped Emma accept her role as Savior. He convinced Regina to open the portal in the well and let Emma and Mary Margaret come through.
Season 3, episode 1 is titled 'The Heart of the Truest Believer.' This is an obvious reference to Henry. If imagination and belief are magic in Neverland then a true believer like Henry will have great power there. In the traditional 'Peter Pan' story Tinkerbell is saved because children believe in fairies. (Everyone clap your hands!) Maybe Henry's belief is needed to save her in Neverland. Or, maybe, quite literally it is his heart that is needed!
Whatever the case, I'm excited to see what happens next. #SaveHenry