Full credits and plot synopses for the films can be found at BFI Screen Online: http://www.screenonline.org.uk/. More extended plot synopses for the books (albeit of variable quality) are on Wikipedia.
A key historical source on the contemporary context is:
Thomson, Mathew (2013) Lost Freedom: The Landscape of the Child and the British Post-War Settlement. Oxford: Oxford University Press
Mandy
Barr, Charles (1977) Ealing Studios. London: David & Charles
Cartwright, Lisa (2008) Moral Spectatorship: Technologies of Voice and Affect in Postwar Representations of the Child. North Carolina: Duke University Press
Kuhn, Annette (1992) ‘Mandy and possibility’, Screen 33(3): 233-243
Kuhn, Annette (2010) ‘Cinematic experience, film space and the child’s world’, Canadian Journal of Film Studies 19(2): 82-98
The Go-Between
Gray, W. Russel (2007) ‘The time in our minds: the presence of the past in The Go-Between’, Journal of Popular Culture 40(4): 643-654
Grossvogel, D.I. (1974) ‘Under the sign of symbols: Losey and Hartley’, Diacritics 4(3): 51-56
Hudgins, Christopher (1996?) ‘Harold Pinter’s The Go-Between: the courage to be’, Cycnos 14(1),
http://revel.unice.fr/cycnos/index.html?id=1238
Klein, Joanne (1985) Making Pictures: The Pinter Screenplays, Chapter 6. Columbus OH: Ohio State University Press
Tashiro, Charles (1993) ‘”Reading” design in “the Go-Between”’, Cinema Journal 33(1): 17-34
Williams, Daniel (2016) ‘Apprentice to deception: L.P. Hartley and the Bildungsroman’, Journal of English Philology 134(1): 43-69
Lord of the Flies
Babb, Howard S. (1970) The Novels of William Golding. Columbus OH: Ohio State University Press
Frank, Erin R. (2010) Lord of the Flies: the educational value of Golding’s text. Pell Scholars and Senior Theses, Paper 58.
http://digitalcommons.salve.edu/pell_theses/58
Singh, Minnie (1997) ‘The Government of Boys: Golding’s Lord of the Flies and Ballantyne’s Coral Island’, Children’s Literature 25: 205-213
The quote by Golding is from: Golding, William (1965) ‘Fable’, in Golding, The Hot Gates and Other Occasional Pieces. New York: Harcourt, Brace & World
The Midwich Cuckoos
Bruhm, Stephen (2006) ‘Nightmare on Sesame Street: or the self-possessed child’, Gothic Studies 8(2): 98-113
Ketterer, David (2000) ‘John Wyndham and “the searing anguishes of Childhood”: from “Fairy Story” to Chocky’, Extrapolation 41(2): 87-103
Ketterer, David (2000) ‘”A part of the… family [?]” John Wyndham’s The Midwich Cuckoos as estranged autobiography’, in Patrick Parrinder (ed.) Learning from Other Worlds. Liverpool: Liverpool University Press
Link, Miles (2015) ‘”A very primitive matter”: John Wyndham on catastrophe and survival’, Irish Journal of Gothic and Horror Studies 14: 63-80
Stock, Adam (2011) Mid-twentieth Century Dystopian Fiction and Political Thought. PhD thesis, University of Durham