(Journal of Toxicology and Environmental Health, Part A) Reasons children are more vulnerable to air pollution: Their lungs are not completely developed, and undeveloped lungs are more vulnerable to assault and less able to fully repair themselves. Pollutants may remain in the lung for greater duration. Finally, higher ventilation rates and mouth-breathing may pull air pollutants deeper into children's lungs, thereby making clearance slower and more difficult. Children also have immature immune systems, which plays a significant role in asthma. The observed consequences of early life exposure to adverse levels of air pollutants include diminished lung function and increased susceptibility to acute respiratory illness and asthma.
Bateson, T., & Schwartz, J., (2007) Children's Response to Air Pollutants, Journal of Toxicology and Environmental Health, Part A, 71:3, 238-243, https://www.tandfonline.com/doi/abs/10.1080/15287390701598234