My theory is that the Others are the button pushers who went psycho and became convinced that their island was the only safe place left in the world and had to be protected against any interlopers who might destroy them. To protect what they see as normal humanity now, that is themselves, they have to perpetuate or increase their numbers while ridding themselves of all the adults who bring the danger from the rest of the world either purposefully or accidentally. The children are preferred because they are "safe," can contribute the genetic diversity to continue the generations, can be conditioned to become loyal to the group with a minimum of resistance or ability to fight back as younger adults could do.

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Things fall apart, the center cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;

--Lines 2-6, "The Second Coming" by Wm. Butler Yeats