The Changes Trilogy by Peter Dickinson
The Weathermonger, 1968.
The Devil's Children1970.
Too famous to really be worth describing I have only two things to say:
1) If anyone out there read them in publication order first, and remembers doing so, I'd really like to talk to them.
2) Someone *please* reprint them! They are as fresh and brilliant as I remember, and astonishingly they haven't dated at all. The last imprint is 2003 in the UK. They need a US imprint and glossy new covers.