The recurring theme of the Others taking children can actually be debunked by considering Goodwin's actions at the tail-section camp. On the first night, three individuals were taken. Presumably, this is because Goodwin had little time after arriving at the beach to judge who was "good" etc. This is supported by Ana Lucia's testimony that 9 more were taken a week later, again presumably after Goodwin has had more time to judge who is worthy of being taken. However, it is notable that the children were kidnapped on the second attack, suggesting that they were not immediately flagged by Goodwin as the theory would argue. Thus, there may be no difference between the children and adults when it comes to making the decision of whether they should be taken, as otherwise they would have been kidnapped immediately on the first night.
The kidnapped children and the children of the Others may be being kept as an isolated group as part of a utopian experiment. The goal being to create a new society by ensuring security from the adults' neuroses and eliminating individuality.
The Others are infertile and cannot reproduce, so they kidnap children on the Island to continue their work.
Assuming the magic boxBen alludes to in "The Man Behind the Curtain" does exist, it would help explain why the children were taken, why Walt was abducted, and why children are so seldom seen at the Barracks. Assuming it works as popular theories suggest, i.e. if you want it bad enough, it will appear out of the magic box, then it makes sense that you don't want kids running around all the time, imagining things the way kids do all the time. Otherwise, the Island would be crawling with dragons, princesses, My Little Ponies, giant robots, and so forth. It also helps explain Ms. Klugh's comment to Walt about going back into the room. Perhaps Walt had a particularly active imagination that made him even more dangerous (polar bears, remember?) So, Walt had to be contained, so very likely he was put into Room 23 to help control his thoughts. Having Walt leave the Island was just as good, as the problem of the kid with the super-imagination causing all sorts of crap from popping out of the magic box was still removed. In any case, children are not seen around the Barracks for this reason: their imaginations are a threat.
Karl was being held captive for the same reason. He is now loose on the Island and is, therefore, a liability.
Maybe all the children before being born wish their mothers were dead.
Children not being raised by their mothers is significent.
This is the reason why Richard Malkin insisted that Claire raise AAron herself.
The result of not being raised by a mother is important to the Others. When finding out that Ben's mother died when he was a baby, Richard became very interested and this is the basis of him letting him join the Others. Alex was forcibly removed from her mother to prevent her from being raised by her, and the same was attempted with Aaron. The Others are interested in Locke partly because he was raised in foster care and not by his mother. The Others lost interest in Walt because he was raised by his mother.
If this is true, it should be noted that Jin, and also probably Shannon, was not raised by his mother. Sawyer was also only partially raised by his mother.
The Names of the childrens might also be important at some point. The son of Jack is David. The son of Claire is Aaron.
Most of the childs seen recently have been boys. This may have something to do with Jacob's candidates.