"in knickerbockers and pantalettes"

Pantalettes were loose leggings worn by women, girls, and very young boys.  They originated in France, and were adopted in Britain and the US. Until the mid-19th century, boys under 8 years old were commonly dressed in dresses, gowns and pantalettes.  Pantalettes for children were mid-calf to ankle-length, worn under shorter skirts.  They could be one-piece or two separate garments, one for each leg, attached at the waist with buttons or laces. They were usually of white linen, and were sometimes decorated.  As boys got a little older, but before they reached puberty, they would graduate to knickerbockers, baggy-kneed trousers, banded just below the knee. 

Diedrich Knickerbocker 1849
Public DomainDiedrich Knickerbocker 1849 - Credit: Felix OC Darley

The term ‘Knickerbocker’ is closely associated with New York.  The surname Knickerbocker originated in upstate New York.  Harmen Jansen van Wijhe invented the surname for himself upon arriving in New Amsterdam around 1682.  The name entered popular consciousness with Washington Irving’s 1809 satirical history book, A History of New-York from the Beginning of the World to the End of the Dutch Dynasty, by Diedrich Knickerbocker. By the 1830s, Knickerbocker had become a local term for an imagined old Dutch-descended New York aristocracy, with knee breeches and old-fashioned ways.