Objective: To examine trends in prescribing psychotropic medications to children and adolescents in Australian primary care from 2011 to 2018. Method: A retrospective cohort study examined prescriptions written by general practitioners using MedicineInsight, a large Australian primary care database, covering approximately 9% of all general practitioner practices. Numbers of patients receiving prescriptions for five main classes of psychotropics (antipsychotics, antidepressants, attention deficit hyperactivity disorder medications, anxiolytics, and hypnotics/sedatives [including benzodiazepines and Z-drugs, but excluding melatonin]) were examined annually by age-group (0–4, 5–9, 10–14, 15–18 years). Melatonin was analysed separately. Results: The number of patients prescribed any psychotropic increased from 25.6 to 36.2 per 1000 individuals from 2011 to 2018 (average annual increase +4.5%, 95% confidence interval [4.1%, 4.9%]; overall +41.4%). Among the five main classes, the largest annual increase was for attention deficit hyperactivity disorder medications (+9.6%, 95% confidence interval [8.8%, 10.5%]; overall +95.8%), followed by antipsychotics (+6.2%, 95% confidence interval [5.0%, 7.3%]; overall +62.8%) and antidepressants (+4.5%, 95% confidence interval [4.0%, 5.0%]; overall +42.8%). Hypnotic/sedative prescribing decreased on average 6.5% per year (95% confidence interval [–8.0%, –5.0%]; overall −40.2%). Anxiolytic prescribing remained steady. Melatonin prescriptions showed the highest increase of all (+24.7%, 95% confidence interval [23.7%, 25.8%]; overall +606.7%). The largest annual increase in antipsychotic, antidepressant or attention deficit hyperactivity disorder medication prescribing occurred in 10- to 14-year-olds (+7.5%, +6.5% and +10.4%, respectively). The largest point prevalence occurred in 2018 among 15- to 18-year-olds, with 98.5 per 1000 prescribed antidepressants. Antidepressants were more frequently prescribed to females; antipsychotics, attention deficit hyperactivity disorder medications and melatonin more often to males. The most prescribed antipsychotics were risperidone (<15 years) and quetiapine (15- to 18-year-olds). Fluoxetine was the most prescribed antidepressant in those aged 5+ years and amitriptyline in 0- to 4-year-olds. Conclusion: General practitioner prescribing of melatonin, antipsychotics, antidepressants and attention deficit hyperactivity disorder medications to under-19-year-olds increased markedly from 2011 to 2018. Although benzodiazepine and Z-drug prescriptions declined, this was offset by a substantial increase in melatonin prescribing.