When minors fight, 'they're still young' is not the whole answer
Classify the behaviour first
Accidental injury during mutual horseplay is treated very differently from a one-sided assault. The key factors are: who initiated physical contact, the nature of the injury, and whether witnesses can confirm the sequence of events.
Who bears responsibility
When a minor causes harm, the guardians (usually parents) carry civil liability. If the incident occurred on school grounds, the school may bear supplementary liability if supervision was inadequate. Articles 1199–1201 of the Civil Code govern this.
Document early
Photograph injuries promptly, keep medical receipts and diagnosis records, and ask the school to produce a written incident report. An official injury assessment is the most useful document when negotiating compensation.