These are findings in a new report, Nutrition Critical, released by Save the Children.
The report showed the impacts of both crises had led to an increase in poverty, a loss of livelihoods, and reduced access to health and nutrition services, pushing up rates of hunger and malnutrition.
The report found that 600 million children world-wide had missed out on vital assistance during both crises.
Jacqui Southey of Save the Children New Zealand said governments must implement child benefits to ease family hardships.
Southey warned the pandemic-related malnutrition could see an average of 153 children die a day over the next two years if action was not taken immediately.
Good nutrition matters, she said.
"It is vital for children to thrive, grow, develop and reach their full potential. And it's also a matter of survival. Good food keeps children alive."
The report found that the pandemic-related malnutrition projected an average of 153 children would die a day over the next two years if action was not taken immediately.
The Pacific had been struck with five cyclones - three of them category 5 storms - since January 2020.
"Even before the pandemic hit, conflict, natural disasters and climate change have led to many communities struggling to provide children with enough healthy food, with one in three children under five suffering from malnutrition," Southey said.
"Families in Fiji, like many others across the Pacific, live on the frontlines of Covid-19 and climate change.
"Increasing drought and water scarcity, rainfall changes, coastal flooding and erosion all combine to threaten children's food security and nutrition."