Well you have come to the right place then for advice.
Firstly I would like to point out it will not damage growth or prevent growth in any way unless it is performed incorrectly.
Seeing as you want to be able to do high kicks I advise dynamic stretches. These should be performed in various different ways; side, front, behind, etc.
A great link to look at to understand what these look like is: web page
I would advise doing most of these dynamic stretches.
Also have you read or can you get hold of Thomas Kurz's 'Stretching Scientifically' seeing as he shows a lot of stretches, which would be rather hard to explain without images.
In the fourth Edition of this book it even has a good workout for kick boxers in it.
It is only a sample workout but he says:
Rotations of joints followed by skipping, and then the dynamic stretches as mentioned.
Knee Kicks followed by roundhouse kicks
This could be paddle drills or kicking a bag
Front lunges, side lunges, isometric stretches, relaxed stretches and jumping rope.
This is pulled straight out of a sample workout in his forth edition book. I think its a great workout but I would advise you to read the whole book before jumping in with any stretches you are unsure about.
You may even want to ask one of you instructors as they will probably be rather flexible. Just ask what they did to become so flexible.
I hope this helps, and keeps you busy for a while. I always used to be rather poor with my high kicks but I felt that the best thing was dynamic stretches as they are very beneficial for kicking.