Bobbsey Twins is a series of children's novels written by American author Laura Lee Hope. The main characters in the series are two sets of fraternal twins, NAN and Bert Bobbsey, and Flossie and Freddie Bobbsey. GEMINI is the astrological sign for twins, which is fitting for the Bobbsey Twins. Flossie and Freddie are the younger set of twins, while NAN and Bert are the older set. Olsen is the last name of the Bobbsey family.