The series was taken off air mid-way through the run, as it was deemed too scary.
The only show I can think of that comes close to this description is the 1984 TV series "The Tripods" which features several children in leading roles and regularly had them traipsing through waterlogged countryside.
The show was cancelled before its finale season but because of poor ratings (e.g. versus the cost of production) rather than because it was too scary
The British post-apocalyptic children's series that was never finished was The Tripods, but that had nothing to do with flooding and was not taken off-air because it was too scary, but simply because the budget was cut.