(http://www.ew.com/sites/default/files/styles/tout_image_612x380/public/i/2012/07/30/falling-skies-harnesses.jpg?itok=zq5H3RuT)
Children are harnessed by the aliens to bring them under their control. It turns them into zombie like slaves, little is known about the harness, however it is part mechanical and part biological, it appears to put metal pins into the childs spine and base of their brain. They can then be controlled by the various aliens and are used as slave labour on their building project. The skitters seems to be very caring towards the children in their care, several have been seen at night sleeping with children protectively embraced by them. Those children under control respond to no stimulus other than the skitters who it is assumed telepathically communicate with the the children. Once a skitter is killed those children under their control will become like zombies until a new skitter arrives.
So far all attempts to remove a harness have resulted in instant death. Those who were harnessed immediately have begun forming scaley skin, the cause of which is unknown. The harness also seems to enhance physical ability with children seen lifting heavy objects while working.