How old are these kids? Because after a certain age it is THEIR responsibility to get up on time, not yours. The best thing is to give them the alarm clock and place it far away from the bed so they have to get up to turn it off. It should be an alarm clock with an annoying tune, it doesn’t matter so much how loud it is. Then, explain that it you will no longer be waking them up every morning, and that it is their responsibility to get to school on time. If they miss the bus or their ride, they’ll have to figure out how to get to school themselves. After one day of missing the bus,(if you don’t cave in and drive them to school yourself) they’ll get up on time.
I know you didn’t want alarm clock ideas, but believe me this works.