This is a school- and family-based prospective trial among Primary/Grade 2-4 (P2-4) students in randomly selected 12 schools in Hong Kong. This study will assess the intervention effects on children's exposure to environmental tobacco smoke (including SHS and THS at home, SHS at home from neighbours and SHS outside home), children's SHS-related knowledge and attitude, intention to smoke, respiratory symptoms, parents' smoking cessation, and family happiness.

Around 12 primary schools in Hong Kong will be randomly selected and recruited and the 3 grades (P2-4) in each of the recruited schools will be randomly allocated to intervention or control arms. After the consenting process and baseline survey, we will conduct a 3-month intervention and then 2-month boosters which include 8 worksheets, around 15 online question quizzes and 30 WhatsApp messages. After 3-month and 6-month follow-up periods, we will assess the differences of children's exposure to environmental tobacco smoke (including SHS and THS at home, SHS at home from neighbours and SHS outside home), children's SHS-related knowledge and attitude, intention to smoke, respiratory symptoms, parents' smoking cessation, and family happiness. According to the results of baseline survey, we will also invite all the students exposed to SHS at home to provide their hair samples before intervention and at the 6th month in order to obtain objective results (hair nicotine measurements).

Aims of this study: (1) To reduce children's exposure to environmental tobacco smoke. (2) To reduce objectively measured exposure to tobacco smoke (hair nicotine) among children who are exposed to SHS at home at baseline. (6-month, laboratory test). (3) To promote SHS-related knowledge and attitudes, and avoidance of SHS among children. (4) To reduce children's intention to smoke. (5) To reduce children's respiratory symptoms. (6) To promote smoking cessation (past 7 days) of parents. (child report) (7) To promote children's perception of family happiness.

We will invite all P2-4 students from 12 schools randomly selected from the 100 schools (which watched the performance by Hong Kong Council on Smoking and Health) to participate in this cluster RCT, as they are able to understand simple questionnaires and other self-help intervention materials, yet remain very receptive to intervention activities from our experience.

Inclusion criteria for hair nicotine test:

1) exposed to secondhand smoke at home from smokers inside home in any of the past 7 days; 2) living with at least 1 smoker; 3) Never smoking or using e-cigarettes.