Walt Lloyd - one of Lost's most mysterious characters, deserves some attention after the information we learned in "Across the Sea". This theory ties into one of Lost's major questions, "What is the significance of the children?" We witnessed the Others ruthlessly steal the children from the tail section's camp in the Season 2 Episode 7 "The Other 48 Days", and we immediately assumed they meant to do the children harm. However, the next and last time we see the children, they're safe with the Others. Since then, we have wondered what purpose did the Others have taking the children? It didn't stop there. They eventually took Walt. We knew that he was special, posessing certain telekinesis abilities (making the rare bird appear and fly into the window, having the polar bear appear, etc), but we didn't know why. Until now.
Season 6 Episode 15. Meet Claudia, an unfornate seafarer who washed up on the Island's shore. It's obvious she is pregnant, and she stumbles upon a crazy woman (Allison Janney) who pretends to help her, act as her midwife, and eventually kills Claudia after she births two boys. Claudia was killed to 'protect' the children - if she had been allowed to raise her own children, they would have been corrupted because she herself was corrupted from living in the civilized world for so long. Protectors of the island must be of the purest breed, bearing no ties to the civilized world. Flight 815 was brought down in an attempt to find a new replacement for Jacob, and young children (as well as unborn children, i.e. Aaron - more on that later) were suited to be the best candidates because of their purity. Within 3 days of the crash, the others had come in the night taking all of the children away from the tail section camp. We can assume that they were all potential candidates, but for whatever reason their candidacy was revoked, possibly because they did not meet Jacob's standards. Moving on to the next youngest, we have Walt in the main camp. Our losties in the front/middle section of the plane were pretty well fortified - established homes, weapons, and a tight knit community. They had to wait for the right moment to snatch Walt, and they did so on the boat when Michael tried to surf his way off the island.
However, the question arises as to whether or not the Others were aware of Walt's abilities or was he just another pure candidate. My guess is the former, and Jacob was aware of this as well. Perhaps Jacob assumed that since Walt already posessed unique powers, he was the chosen one. However something happened between the time the plane crashed and the time that Walt was taken - Walt grew to love his father. Walt even said to Michael - "I hate you," when Michael forbade him to hang out with Locke. But eventually Michael won over Walt's heart, and even though everybody was happy in Lloyd and Dawson town, this presented a problem for Jacob. Walt now had a 'tie' with his father, thus becomming unpure and unable to fulfil the duty of protector of the island. The protector has no other purpose in life other than watching over the island - no friends nor family. Jacob would not be able to pursuade Walt to take over beacuse Walt would not give up his newfound love of Michael to watch over some island.
Next up is Aaron, the youngest member of the island roster (Ji Yeon Kwon doesnt count - she wasnt born on the island). Aaron would have made an exceptional choice as island protector since he was a baby just like MiB and Jacob. Jacob knew this, and the injections they gave to Claire were to ensure Aaron's safety. However, MiB intervened, lured Claire away by posing as Christian, and disrupting the natural order of things. MiB as we know can't kill the Losties, so this was his logical move - to seperate the two, leaving Aaron with the Losties, having them care of Aaron and taking him with them when they left the island. This was the next best thing next to killing a baby - to get Aaron, the potential candidate, off the island for good.
APPLYING THIS THEORY TO THE REMAINING CANDIDATES
Flash to the wall in the cave with the names on it. We can rightfully assume that a few of the names were that of the children, but since there were no children left Jacob had to resort to the only ones he had left. Season 6 has been all about Jacob manipulating the last few candidates to fit the role of protector, and we must consider who is most likely to fit the bill. The most obvious choice is Jack, since he had no ties in the real world anymore, to the point where he almost committed suicide. He went from man of science to man of faith, believing whole heartedly that John Locke was correct in saying that he had to protect the island. Jack was the only one who refused to leave the island when everyone else was going on the submarine, which is exactly what Jacob wanted all along. Now all Jack has to do is 1) Kill MiB and 2) discover the awesome light under the island, realize its significance, and devote the rest of his life to protecting the island. no big deal, right?