The 1901 census and 1911 census are very interesting. In 1901 there are 2 families of Kilkey and one family of Kilky. By 1911 two families that were Kilkey have changed to Kilkie.
Another family in the 1901 census, named Small was found again renamed to Kilkie in 1911. The family is recorded as living in Slaghmanus, just outside Derry city and near all other known Kilkie residences. In my early days researching the name I saw references to Small being the same as Kilkie, but cannot find official references at present. A connected fact is that a Scottish son of the irishman Thomas Kilkie of Clondemot was named Thomas Smalls Kilkie (born in Glasgow in 1869). There is no direct relation that is known with the name Smalls and the name disappears after this individual. More research is needed.