The Hollies never got around to recording it and so he brought the song to his next band, Crosby, Stills and Nash. The trio recorded the song but when it was released in 1970, the band had added Neil Young so the album was CSNY's "Deja Vu," but Young doesn't play on the song.
In fact, here's a nice version by Crosby Nash (no Stills or Young):
The idea is that you write something so personal that every single person on the planet can relate to it. Once it's there on vinyl it unfolds, outwards, so that it applies to almost any situation.
Clearly, the song had autobiographical meanings for him. I didn't find anything specifically about the song, but in this 1974 Rolling Stone interview, Nash talks about his father. The elder Nash bought a camera from a friend. The police showed up and claimed the camera was stolen property and demanded Nash's father to reveal who had sold it to him; when he refused, he was sent to prison for a year. Nash claims the episode so shamed his father, it essentially caused his death.
Somewhat ironically, given the significance of a camera in his father's demise, Nash is a proficient photographer, as well as a collector of photographs. The first photograph he bought was Diane Arbus' "Child with a toy hand grenade in Central Park, NYC 1962"; as he explained in a 2006 interview with the San Diego Union-Tribune, he had just recorded Teach Your Children and the sight of a boy with toy weapons seemed to encapsulate what he was trying to say with his song.