More than 1000 children are living in evacuation centres in Fiji due to Cyclone Mick.
UNICEF says 3600 people, including 1500 aged under 18 years, are still in evacuation centres.
The agency says many are still recovering from a severe flood last January.
Pacific deputy representative Tim Sutton says an outbreak of water-borne disease continues to be a major risk due to polluted waters. Children under five years are the most vulnerable.
The cyclone on Monday is believed to have caused five deaths.