Laura Lee Hope 
The Bobbsey Twins on the Deep Blue Sea 

The Bobbsey Twins are the principal characters of what was, for many years, the longest-running series of children’s novles. The books related the adventures of the children of the middle-class Bobbsey family, which included two sets of fraternal twins: Bert and Nan, who where 12 years old, and Flossie and Freddie, who where six.