They visited at the same time as a girl from Birmingham who died from E.coli poisoning and two other children who contracted the bug.
The father of the three latest victims said:"I thought they were going to die." Peter Haynes, who lives near Exeter, said his son was in so much agony it was "heart-rending".
It appeared the youngest child infected the other two, said Dr Gill Lewenden, South and West Devon Health Authority's consultant in communicable disease control. The E.coli they suffered was of the same strain as the three other affected families, she said.
The source of the infection still has not been identified, but there is no increased risk, she said. "Whatever happened was a short-lived episode."
The health authority rejected claims by an environmental group that sewage leaking on to a beach could have been the source of the outbreak. South West Water admitted that on 24 July sewage-related debris was washed out and that some flowed across a path on to the beach.
But Brian Jones, the chief executive of Teignbridge council, said analysis of sand, seawater and seaweed showed no trace of E.coli at the Warren, which boasts a Blue Flag, Europe's top category for cleanliness.Reuse content