notice how their clothes are growing, living out new dreams ready to be a part of something bigger, no longer attached to dead weight. watch their skeleton collapse from neutering their ambitions
ask, "are you okay?" don't listen for the answer stare past them at the wall wonder what's for dinner teen depression is a myth, anyway.
give a sympathetic smile "i've been blue before, too." no worries, they're probably just tired probably just hungry probably just bored
tell them to get a good night's sleep and eat a hearty breakfast so they don't become one of those poster children, a beautiful soul "gone too soon" that'll fix it.