A 7-year-old boy is brought to the paediatric psychiatry clinic by his mother with complaints of inattention and hyperactivity for the past 2 years. The teacher reports that he frequently leaves his seat during class, interrupts others, and struggles to complete assignments. At home, he is restless, talks excessively, and has difficulty waiting his turn during games. His mother reports he was born at term with no perinatal complications. On examination, he is alert and oriented but fidgety. Cognitive testing shows average intelligence. The child meets DSM-5 criteria for ADHD, combined presentation. His parents ask about pharmacological management. Which of the following is the first-line pharmacological agent for ADHD in children?