Urban air pollution affects the health of hundreds of millions of people around the world. In SE Asia, 800,000 deaths were attributed to particulate air pollution (PAP) - the tiny dust particles that pollute the air - in 2012, alone. This is a particular issue for children because early exposure is directly attributable to life-long vulnerability to respiratory diseases. Finding appropriate, sustainable and innovative mechanisms for their protection is essential to ensuring resilient and productive societies in the future. This is the primary challenge to which the FACE-UP project responds. Airborne particulates are hard to avoid. They not only pollute outdoor air, but also contaminate the indoor environment so children are exposed at home and school, as well as during outdoor travel, play, and exercise. Reducing exposure to PAP is one of four crucial actions identified by our partner UNICEF in their framework for improving children's health. The best way to reduce exposure is to curb the production of pollutants (known as emissions reduction), but this is a slow and difficult task involving profound shifts in policy, legislation and infrastructure. Until air quality reaches safe levels, governments and NGOs must 'face-up' to the fact that communities are taking protection into their own hands, commonly through wearing facemasks, which may not be effective for children. Those who exercise their right to protect themselves and their children must be provided with the best evidence on how to do this in ways that are affordable, accessible and, crucially, complement their cultural environments. A key goal of FACE-UP is to elucidate how local factors affect the way that communities can protect their children from PAP, and to harness this information to ensure that appropriate advice and support can be freely accessed and, where appropriate, policies enacted to alleviate risk. FACE-UP is a consortium of PAP exposure, social, behavioural and health scientists, statisticians and local and international agencies whose expertise lies in the interrelationship between the environment and children's health. We will work with urban children in two developing countries, Indonesia and Nepal, which both exhibit severe PAP but have differing contexts, being home to different cultures, climates, socioeconomics, built environments and policies. These factors not only impact the potential for ill health, but people's motivation, opportunity and capability to reduce children's exposure to PAP. We will determine how, when and where children are exposed, as well as current protective measures (if any). Sensitive to, and influenced by, the feasibility of different practices, we will develop and assess the effectiveness of different types of protective actions, such as behaviour changes at home and school, and personal actions like wearing facemasks, and will estimate the potential health impact that can be achieved through adoption of these practices. Working with the communities to capture primary data on their cultural contexts, the project will also seek to understand the logistical factors that influence uptake (e.g. availability of education, political barriers and material supply chains) and how people might best learn about the practices. Ethical issues of agencies recommending practices that may not be very effective or affordable also will be evaluated. Robust data collection and analysis will feed directly into co-created and evaluated solutions, such as informational products, in partnership with local children, carers and agencies, which will be disseminated locally and globally, facilitated by our partner organizations. The FACE-UP evidence will support ethical policy decisions, and individual actions to implement interventions, so that, combined with emissions reduction strategies, the world's children will grow up with the evidence to reduce their risk of developing diseases from air pollution exposures.