sci fi childrens book

[mandimoo]

mustve been from approx early 80's. one or more children are transported to different lands by a magic stone. (im talking more stonehenge stone than a discarded rock). one place they went was very futuristic and a child fell out of a flying car. he was horrificly injured, but because of their modern medicine they were able to make him better. i remember it being quite a dark story and there may have been more than one book, a trilogy perhaps?

[tickledtrout]

Could it have been 'The Dark is Rising' sequence by Susan Cooper?