Sleepy Time Jars- Put a pom pom into the jar every time they take a good nap or go to bed without complaining or getting up. When the jar is full they get a "prize" or treat of their choice. My mom used to do a similar activity called a star chart.
Screen time is an app that lets you limit time your child/student uses iPhone or iPad. You set the time, press start, and pass it to your kiddo. When time expires, it stops the game! There's an app for everything!