This show Is Adapted from the famous Enid Blyton's books 'The Famous Five', the series filmed in summer 1995 and 1996 was not the first one. The first adaptation : a film in 1957
The first Tv series : 1978. 
In 1978, the action was set in the 70's, whereas in the 1996 series, the action was set in 1953. It means to say, the decade when the original books have been written.