While not a "one size fits all" solution, cognitive behavioral therapy (CBT) is a great starting point for many concerns, from anxiety to depression, eating issues, and substance use.
CBT is considered a gold standard form of treatment by the American Psychological Association. Based on the idea that thoughts, feelings, and behaviors are all related, CBT provides individuals with the tools to change the way they think, which (as the thinking goes) will then impact emotions and actions in daily life.
A therapist will adapt basic CBT approaches based the age, developmental level, and concerns of a particular client. The overall goal is to improve the way the client copes with stress, disappointment, and life challenges, so the client (and perhaps their parents) have the tools, and the therapist becomes unnecessary!