Hide and seek was a game often played by children.
On at least one occasion, Rory Williams played hide and seek with Amelia Pond and Mels. He hid for hours while Amy and Mels neglected to look for him as they were talking about Amy's imaginary friend. When confronted about this, Amelia told Rory that they just hadn't found him yet. (TV: Let's Kill Hitler)
When Gwen Cooper arrived at the Hub to tell Jack Harkness about a lead she found on Jonah Bevan and accidentally walked in on him and Ianto having sex, Jack said that they could have used her during "naked hide and seek." Ianto told her that Jack always cheats. (TV: Adrift)