Background Anxiety related to the dental context is a clinically significant challenge. In children, dental fear is often accompanied by disruptive and uncooperative behaviours that can render treatment difficult. Although techniques to reduce children's anxiety exist, many have not been formally evaluated. Design Diaphragmatic breathing has been shown to reduce fear and anxiety, but few investigations have evaluated whether it can reduce dental anxiety in children. This crossover study tested the effectiveness and feasibility of diaphragmatic breathing in twenty children undergoing dental care. Results Compared with the treatment as usual, such a simple technique had significant benefits on mood, self‐reported pain and autonomic balance, thus reducing sympathetic activation. Conclusion Diaphragmatic breathing is a low‐cost, easy–to‐implement technique suitable for daily dental practice, and is a promising tool for reducing negative effect and physiological distress in children with dental anxiety that results in more cooperative behaviours and reduced visit time.