Five Were Missing — Lois Duncan

IT WAS AN ORDINARY SCHOOL BUS RIDE
…at first, Glenn was being his usual wonder-boy self, while his brother Bruce quietly sat in his shadow. Shy, dark-haired Jesse French tried to concentrate on the book she was reading. Dexter, sullen and self-conscious about his handicap, sat alone. Marianne Paget was talking about her parents' divorce.

But suddenly they knew something was wrong. They were the last five left on the bus…and the bus wasn't stopping. It was incredible. It was impossible. But it was happening -- they were being kidnapped.