Devon and Cornwall Police said the family from London was on holiday in Cornwall over the Bank Holiday weekend when the accident happened in the Camel Estuary near the picturesque coastal town of Padstow.
A 39-year-old woman, a four-year-old boy and two girls aged 10 and 12 were airlifted to Derriford Hospital in Plymouth, where they are being treated for "a range of injuries, some of which are life changing", police said.
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