I would start by explaining why all tissues need stress to regain and maintain health (explain fragility and antifragility). This includes our joints. How
we exercise the joints is the important thing to learn. Most athletes retire, not because of muscle problems or getting older per se, but due to joint problems: a bad back, bum shoulder, trick knee, hip damage, etc. These are the areas we target in Yin Yoga, but through a safe form of exercise: not rapid movement of the joint, but long held, static stresses, which is like applying a traction to the joint.
I generally believe that children, who are in the yang time of life, need yang exercise, but you are dealing with a population of people (teens) who are already yang, so my concerns is not as great for them. Athletes' injuries range from mild and annoying (a muscle strain) to painful and chronic (tendon and ligament sprains) to career ending (usually, severe joint damage.) Yin yoga won't help the first of these injuries, but rest and massage may, but Yin Yoga may help with the last group: joint problems. As we know, all tissues need exercise, even damaged tissues. When a joint is damaged, there exists the possibility of doing too much to the joint and making matters worse, but to do nothing just guarantees that the joint will atrophy. So, some yin--yes! How much yin? Don’t know.
This is where it becomes very valuable for you, as the teacher, to help your teen students learn their own bodies: their limits, what works, what signals to attend to and when to back off. You can apply yin stresses to all the joints you want to target, to help stress the cartilage, ligaments, joint capsules and bones, but keep asking the students to attend to what the body is saying. Not just now while in the postures, but as they come out, and the next day. Start easy, pay attention, if safe move up the antifragility curve
slowly so that you don’t go too far.
There is no one prescription that will work for every athlete: but with attention and intention you can help them discover what might work for them.