It looks as though The Lives of Christopher Chant came out in 1988, so I would have been 14 and I suspect if I'd encountered it then I would have read it, but by that stage I wasn't looking at the "children's" sections in the library and bookshops any more (and I think it often took libraries a while to get books, anyway - I suppose it wouldn't have come out in paperback until a year or so later). That was about the time I read both Howl's Moving Castle and Fire and Hemlock, but they were both (re?)published in Methuen's "teen" imprint rather than the "children's" imprint so I found them in the YA section of a bookshop.