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Hey julieb, thanks for your input.
I was actually searching for the information today (and to make sure i wasnt going mad!) and found out what it was.
It was called Childrens Island and It's set during World War 2 when some British children are invited to live in the United States by the President's son.
However, the ship they are traveling on is attacked by a U-Boat and sunk. The authorities believe they have all drowned, but several children survive the attack and eventually find themselves stranded on a small island.
The series consists of them living on the island and having to deal with their situation (and some hostile monkeys).
All the while they are there, the President's son never gives up hope that they have survived. In one episode a fighter plane crash lands on the island and the children use the plane's radio to try and get help. However the only person to hear their mayday is the President's son himself, who happened to be on a yacht at the time. People think the Presiden't son is delusional and he is then sedated.
Finally found it after years of searching!
Thanks for your help