I think this is one of those films which works better in black and white. The children with their blond hair are all the more sinister.
Beginning with cosy very English scenes of sheep grazing and George Sanders standing by a fireside, the mood very quickly changes.
The initial joy felt by one of the mothers, played very well by Barbara Shelley, soon turns to fear as she wonders just what sort of baby she has given birth to, though she still retains the love of a mother for a child. The suspence builds as it becomes obvious what a threat the children are becoming. It slows just a little in the middle but has a satisfying and tense ending.
I saw this many years ago and was so pleased to be able to get it on DVD. The second film is disappointing.