DESIGN: Data from the SEANUTS II cohort were used. Questionnaires, including a COVID-19 questionnaire, were used to study the impact of the pandemic on parents/guardians and their children with respect to work status, household expenditures and children's dietary intake and lifestyle behaviours.

SETTING: Data were collected in Malaysia, Indonesia, Thailand and Vietnam between May 2019 and April 2021.

PARTICIPANTS: In total, 9203 children, aged 0·5-12·9 years, including their parents/guardians.

RESULTS: Children and their families were significantly affected by the pandemic. Although the impact of lockdown measures on children's food intake has been relatively mild in all countries, food security was negatively impacted, especially in Indonesia. Surprisingly, in Malaysia, lockdown resulted in overall healthier dietary patterns with more basic food groups and less discretionary foods. Consumption of milk/dairy products, however, decreased. In the other countries, intake of most food groups did not change much during lockdown for households based on self-reporting. Only in rural Thailand, some marginal decreases in food intakes during lockdown persisted after lockdown. Physical activity of children, monthly household income and job security of the parents/guardians were negatively affected in all countries due to the pandemic.