Paul does not speak until almost an hour into the movie.
Ron Goodwin had already composed the score for the predecessor Village of the Damned (1960) and returned for this film.
U.S. Naval Activities, London came about in 1951 as a joint military support effort between the U.S. and the UK. This arrangement lasted until 2007; thus, it was entirely possible to see a 'U.S. Navy Exchange' truck motoring around in London in the 1960s. While this truck's presence is not clear in the storyline, there could be a connection to the united effort by the embassies to deal with the foreign children who have the supernatural powers.
Filmed in the spring of 1963.
Ian Hendry and Alan Badel play two flatmates in the film. As it was made at a time when homosexuality was illegal in the United Kingdom, there could be no inference that they were anything other than platonic friends.