(aka I attempt to make sense of at least SOME of today’s metric assload — yes this is a scientific measurement —of spoilers)
So, we’ve known for a while that the Charmings have some kind of dark secret that is supposed to change how you view them in the entire series, starting back in season 1. We also know that we’ll see them dealing with the QoD in the EF prior to the first curse in the next episode. We ALSO know that whatever this secret is, they don’t want Emma finding out at any cost.
SO: here we go. Maleficent and King Stefan, Aurora’s father, had an affair, and this resulted in Maleficent going after his wife, Aurora’s mother, somehow. (In 2x01 when he wakes her up with TLK, Philip reassures Aurora that Maleficent can’t find them here, and she refers to something Maleficent did to her mother, if I’m not mistaken. In 1x02 back when we met Maleficent for the first time when Regina was getting the Dark Curse from her, Regina also implied that Maleficent had gone after Aurora’s mother). A child, Lily, is born of this illicit affair. At the same time, Snow and Charming are trying to broker some kind of deal with the QoD to stop the curse, which the QoD for whatever reason aren’t interested in doing — maybe they don’t think Regina can/will actually do it, etc. Who knows. So, and once again this is just me spitballing in the dark, Snow and Charming are somehow responsible for taking Lily away from Maleficent and sending her to the LWM — as payback, as incentive, as something. Maybe she goes with the curse, maybe she goes before, who knows. But anyway, as a result of Snow and Charming’s direct agency, Maleficent loses her child.
About 15-odd years later, Emma and Lily (who are obviously about the same age) meet in the LWM. Snow and Charming’s daughter who they didn’t want to give up, and Maleficent’s daughter whom Snow and Charming took away from her. Emma leaves Lily, and obviously doesn’t think much about her at all until she sees her on the videotape with Ingrid. Snow and Charming don’t recognize Lily because she was just a baby when they last saw her, and why would they think that anyway? And since Maleficent is dead, or dragonified and/or in ashes under the library, they are confident the secret is safe. But now Cruella and Ursula, who know about the switcheroo/baby-napping, are coming to Storybrooke. RUH-ROH.
In other words, this would push all of Emma’s buttons at once. She’s still getting used to the fact that her parents chose to give her up and send her to the LWM alone, but has more or less accepted that it was for the “greater good.” But now if she finds out that they willingly did that to another child, it would ROCK her. Especially since said child was someone she met and ALSO left behind. It would tarnish our idea of Snow and Charming who only ever made selfless choices — they made the choice for someone else that they wanted to avoid at all costs, i.e. forcing another magical girl away from her parents to grow up alone in the LWM. In other words, they basically used Lily as a sacrificial lamb and yet that didn’t even work and she STILL had to grow up without them.
So yeah. This is the theory I’m going with until it’s disproved in next week’s ep. Heh.