Nephew

In family, nieces and nephews were the children of one's sibling. (TV: Children of Earth: Day Four)

David Davies was the nephew of Ianto Jones, being the son of his sister Rhiannon Davies. (TV: Children of Earth: Day Five)

Major Cal Kilburne deceitfully claimed to be the nephew of "Aunt" Sarah Jane Smith to Gita and Haresh Chandra. (TV: Enemy of the Bane)