John Zimmerman, an associate professor at Carnegie Mellon University, has developed a clock to keep young children sleeping.

The Reverse Alarm Clock consists of a moonset and sunrise calculator, a small circular wall-mounted unit that is set by the parents.
A "Treasure Chest Music Selector" is also incorporated in the clock, allowing children to select bedtime and wakeup music, furthering the emphasis on responsibility and routine.

The moonset and sunrise calculator controls a "sky display," illustrating time in a way that young children can understand by using images of the sun, moon and stars. When the moon is lit, the children should stay in bed; when the moon is off, the children can get out of bed if they wish but not disturb their parents, if possible. Finally, when only the sun is on, the wakeup music plays and they kids must get up and start the day.

In case you wonder if this clock works, the team around Zimmermann conducted various studies that showed that this alarm clock actually works.

There is no information available yet if the Reverse Alarm Clock will become available as a commercial product.
Via this CMU press-release. Looks like universities are a great breading ground for alarm clocks. See also MIT's Clocky.