I love this topic! My younger two are 5 and 8. I bring hot chocolate and let the smell get to them. I tell them if they don’t get up, the hot chocolate will get cold and they won’t get another one. That usually works.
Odd suggestion: what about not interfering at all? Maybe the kids are relying on you to wake them up rather than building in their own internal alarm clocks? Make arrangements with the school to give the kids extra homework, tests, or just plain dock grades for lateness and absence. Then let the kids learn to wake themselves up. It might take a week, but the harsher the consequences, the likelier their motivation will peak.
At the same time, every time they are up on time, have an awesome breakfast waiting for them. If they don’t make it down to the kitchen, eat it yourself!