The slightly redundant twins in THE RUNNERS raised the entire historical question of TWINS IN KID-LIT: whence it came and where it went — A.Ransom’s various gangs and combos delivered one early set: Port and Starboard in Coot Club and The Big Six; Blyton girlschool stories often featured a twins; but the motherlode was the slightly nutty 26-book oeuvre of LUCY FITCH PERKINS (1865-1937) viz:
The Dutch Twins (1911): Kit and Kat (short for Christopher and Katrina)
The Japanese Twins (1912): Taro and Take (pronounced “tah-kay”)
The Irish Twins (1913): Larry and Eileen
The Eskimo Twins (1914): Menie and Monnie
The Cave Twins (1915): Fire-Top and Firefly [this one i have read]
The Mexican Twins (1915): Tonio and Tita (short for Antonio and Margarita)
The Belgian Twins (1917): Jan and Marie [more LFP at proj.gutenberg]
The French Twins (1918): Pierre and Pierrette
The Spartan Twins (1918): Dion and Daphne
The Scotch Twins (1919): Jean and Jock
The Italian Twins (1920): Beppo and Beppina
The Puritan Twins (1921): Nancy and Daniel
The Swiss Twins (1922): Leneli and Seppi
The Filipino Twins (1923): Ramon and Rita
The Colonial Twins of Virginia (1924): Tom and Trix (short for Thomas and Beatrix)
The American Twins of the Revolution (1926): Sally and Roger
The Pioneer Twins (1927): Jim and Josie
The Farm Twins (1928): Tommy and Nancy
The Norwegian Twins (1933): Eric and Elsa
The Spanish Twins (1934): Carlos and Felipe
The Chinese Twins (1934): Golden Boy and Moon Flower
The Indian Twins (1938): Pigeon and Beaver Boy
The Dutch Twins and Little Brother (1938) Kit and Kat
(plus — date unknown):
The Pickaninny Twins
Kit and Kat
The American Twins of 1812