This is a practical guide designed to help practitioners and advocates apply behavioural science to protect children from environmental health threats. Grounded in evidence and real‑world experience, the guide translates behavioural insights into actionable strategies that can shift norms, improve risk communication, and drive healthier choices at individual and community level. REACH supports child‑centred approaches that make invisible risks visible—and turn awareness into sustained action for healthier environments where children live, learn, and play.