Ian Gillan has said that "Child in Time" is based on It's a Beautiful Day's psychedelic song "Bombay Calling". It's a Beautiful Day in return borrowed Purple's "Wring That Neck" and turned it into "Don and Dewey" on their second album Marrying Maiden (1970). As Ian Gillan put it in a 2002 interview, "There are two sides to that song - the musical side and the lyrical side. On the musical side, there used to be this song 'Bombay Calling' by a band called It's A Beautiful Day. It was fresh and original, when Jon was one day playing it on his keyboard. It sounded good, and we thought we'd play around with it, change it a bit and do something new keeping that as a base. But then, I had never heard the original 'Bombay Calling'. So we created this song using the Cold War as the theme, and wrote the lines 'Sweet child in time, you'll see the line.' That's how the lyrical side came in. Then, Jon had the keyboard parts ready and Ritchie had the guitar parts ready. The song basically reflected the mood of the moment, and that's why it became so popular."
"Child in Time" is an essentially simple composition, featuring an organ intro, three power chords, and a two minute long guitar solo. Lyrically dark, vocalist Ian Gillan utilizes his wide vocal range and goes from quiet singing to loud, high-pitched, banshee-esque screaming. Guitarist Ritchie Blackmore comes in with a slow solo, which builds up to a fast-pace playing and then ends abruptly, with the whole song cycle starting over again. Blackmore is normally associated with playing a Fender Stratocaster, however, he played a Gibson ES-335 on the studio version of the song.
A staple of the Deep Purple live concerts in 1970–73 and later after their initial reunion tours of 1985 and 1987–88, the song has not been featured regularly at concerts since 1995. Gillan cites many personal reasons for leaving the song out, but it is likely that, given his advancing years, the song is becoming increasingly difficult to perform without sampled vocal backings. Its last appearance in Deep Purple's live set was at Kharkov's Opera Theatre's scene in 2002. In that performance, high-pitched guitar was used to cover up Gillan's then-limited vocal range during the "screaming" parts. A similar technique is used on current live performances of "Space Truckin'".
A live version later appeared on the 1972 live album Made in Japan. Another live version can be found on the Scandinavian Nights / Live in Stockholm live album, recorded in September 1970. Gillan also featured a live jazz influenced version of the song in his Ian Gillan Band project of the late 1970s.
"Child in Time" was ranked no. 1 on Radio Veronica's "Super All-Time List" in 1989. The song ranked at no. 16 in Guitarist's 1998 readers poll of Top 100 Guitar Solos Of All-Time. English disc jockeyJohn Peel's 1976 list of Festive Fifty featured the song at no. 25.
- The song was covered by Yngwie Malmsteen on his 1996 album Inspiration.
- Jon Lord's solo organ introduction was sampled by Big Audio Dynamite and used in the introduction to their song "Rush".
- A portion of this song was featured in the 1996 films Twister, Breaking the Waves and in 23.
- The song is used in the 1999 documentary One Day in September, which is about the 1972 Munich Olympics hostage crisis. It plays during a rapid montage of the violent aftermath of the concluding airport shootout.
- This song was used in the finale of Bottom Live 2003: Weapons Grade Y-Fronts Tour as Eddie and Richie begin traveling back in time to the dawn of time.
- The song was covered by Cactus Jack on their 2003 album Deep Purple Tribute.
- A new truncated version also appears on 2006 studio album The Village Lanterne by Blackmore's Night, titled "Mond Tanz / Child in Time".
- A portion of this song was featured in the 2008 film Der Baader Meinhof Komplex.
- A portion of this song was featured in the 2007 BBC television documentary The Secret Life of the Motorway, in the last programme of the 3 part series.
- The song was covered by Rata Blanca and Tarja in a show in Buenos Aires on 9 June 2009.
- The song is available as downloadable content for the music video game Rock Band 3.
- The intro of this song was used as basis for the U.U. intro-version of the Exterminate! (song) performed by the German dancefloor project Snap!