How old are they? With our DS9, we have set up an alarm clock and make sure it's set each morning. When (if? ha, not often yet this school year) he doesn't get up when it goes off, we note how tired he is and tell him that evening that's why he needs to go to sleep when we say, not when he finishes 100 more pages.
Beyond that, we do showers right after dinner time, so that's done and isn't a winding up factor. They are in PJs and are in their rooms. DS5 gets a story and his lights go off at 7. With any luck, he's off to sleep shortly thereafter. DS9 stays in his room and reads until we come in to say goodnight, remove his book (and glasses!), turn off the light. That helps.
