Secondhand smoke (SHS) is caused by burning tobacco products that emit up to 7000 chemicals and over 70 carcinogenic compounds. Thirdhand smoke (THS) is solid residue remaining on furniture and carpets, including suspended particles derived from a burned tobacco product. Exposure to these compounds occurs through inhalation, oral ingestion, or dermal uptake. Examples of the tobacco smoke pollutants can include nicotine, benzene, naphthalene, formaldehyde, and nitrosamines related to tobacco. Exposure to SHS and THS are preventable. Infants and young children suffer disproportionately from tobacco-related pediatric disease since they spend much of their time indoors in households and cars. Despite growing awareness of the need to protect children from exposures, a recent survey reported more than 50% of children aged 3 to 11 were exposed to SHS. Although school-based health interventions have targeted healthful nutrition and physical activity among preschoolers and kindergarten, data are scarce for school-based activities addressing prevention of exposures to SHS and THS among those aged 4 to 6. We describe the design and future testing of such an intervention. This will be a pilot randomized controlled trial designed to evaluate the feasibility of conducting an intervention for teaching children to protect themselves from exposure to SHS and THS. We will use a mixed methods approach. Qualitative methods will be used to determine perceptions of classroom teachers and student participants aged 4 to 6 about refining the intervention before the feasibility trial. During the trial, three preschools will be recruited for a total of 12 classrooms and randomized to either control or intervention curriculums. The control classrooms will receive a mathematics curriculum. The intervention classrooms will receive a curriculum about awareness and health consequences of exposures to SHS and THS. The primary outcome is the feasibility of conducting the intervention, including recruitment and retention of participants from pre-k and kindergarten classrooms. Two exploratory outcomes will be effectiveness among child participants and acceptance and response of the parents to the intervention. We will evaluate program effectiveness with the Preschool Health and Safety Knowledge Assessment, a reliable and valid measure for gauging the effectiveness for teaching health and safety knowledge. The story depicted in the intervention program chronicles how the main characters identify and successfully avoid SHS and THS. Activities are designed to allow children to play and discover "clean and dirty air." If the study is successful, we anticipate pursuing external funding sources for conducting a large group-randomized controlled trial. Future intervention iterations will incorporate the use of technology.