His behaviour is sometimes childish. The underlined word means

The correct answer is Option A (like a child-in a bad sense).

Key Points:
• Distinction between 'Childish' and 'Childlike' in English morphology and semantics.
• 'Childish' carries a derogatory/pejorative meaning: immature, foolish, petulant, or silly (like a child in a negative sense).
• In contrast, 'Childlike' carries an appreciative/positive meaning: innocent, pure, trusting, or candid (like a child in a good sense).
• Therefore, 'childish' specifically denotes 'like a child - in a bad sense'.
• Key Takeaway: 'Childish' means immature/silly (like a child in a bad sense), while 'childlike' means innocent (in a good sense).