Child (Children of Earth: Day Four)

A human child once lived in the Holly Tree Lodge orphanage in 1965. At that point, Andrew Staines, Ellen Hunt, Michael Sanders and Jack Harkness made a deal with a race called the 456, and the deal was for the aliens to take twelve children from the orphanage in exchange for an anti-virus for influenza. The child, along with eleven others was taken from the orphanage and were teleported away from somewhere in Scotland.

This child was then connected to the aliens' ambassador, and it fed off the "hit" that the child gave to it. When the ambassador later visited Earth, the child was still connected and since being taken hadn't aged at all. According to the ambassador, the child would "live forever", but was fully conscious of what was happening. The child apparently died when the ambassador was attacked by its own radio wavelength, that Jack used against it. (TV: Children of Earth: Day Four)