First, inform yourself about the school system in this country, it is only comparable to Austria and main parts of Germany, and something tells me you are neither Austrian nor German.
Secondly, there are several types of schools, so forget anything you know about "high school" or any concept like it, because you will have to consider things from different perspectives.
Last, keep cool. If your children will follow Swiss curriculum, take it from where they are now: their age. Then you get first hand information about future possibilities from the school, you can change and transfer and take "bridge" exams and so on.
Now click on those links listed here and read with a cup of tea, or latte, or coffee, or mate, or ovomaltine... whatever helps relaxing in your culture.
LOOK HERE FIRST for Childcare/Schooling / Family Info / Help Sites