“Dango” is a Japanese sweet dumpling made from mochiko (rice flour), and usually served in a group of at least three on a skewer or stick. “DANGO, n. A dumpling” was printed in A Japanese and English Dictionary (1867) by James Curtis Hepburn.
 
It’s uncertain when dango became a sweet dessert or snack. “Japanese dango, (a sweetmeat made of mochi rice with ‘an’ otherwise known as black sugar locally)” was printed in the Honolulu (HI) Advertiser on December 2, 1955. “Dango, a Japanese pastry made of special bean paste and mochi rice” was printed in the Honolulu (HI) Star-Bulletin on August 10, 1964. The Shirokiya store at Ala Moana Cente in Honolulu advertised cooking demonstrations of dango in 1972, 1976 and 1977.
   
The song “Dango San Kyodai” (The Three Brothers Dango) became a popular fad in 1999.
 
   
Wikipedia: Dango
Dango (団子) is a Japanese dumpling and sweet made from mochiko (rice flour), related to mochi. It is often served with green tea. Dango is eaten year-round, but the different varieties are traditionally eaten in given seasons. Three to five dango are often served on a skewer.
           
Google Books
A Japanese and English Dictionary; with an English and Japanese Index
By James Curtis Hepburn
Shanghai, China: American Presbyterian Mission Press
1867
Pg. 48:
DANGO, n. A dumpling.
 
Google Books
A Handbook of Colloquial Japanese
By Basil Hall Chamberlain
London, UK: Trubner & Co.
1888
Pg. 417:
dango, a kind of dumpling.
   
Google Books
Transactions of the Asiatic Society of Japan, Volumes 18-19
By Asiatic Society of Japan
1891
Pg. 507:
JAPANESE FUNERAL RITES.
BY
ARTHUR HYDE LAY
(Read 8th April, 1891.)
Pg. 531:
Last of all came servants bringing dango, dumplings, impaled on spits, and cakes, which were afterwards distributed among the bystanders.
   
Google Books
Glimpses of Unfamiliar Japan, Volume 1
By Lafcadio Hearn
Boston, MA: Houghton, Mifflin and Company
1895
Pg. 107:
These offerings consist of the foods called somen, resembling our vermicelli, gozen, which is boiled rice, dango, a sort of tiny dumpling, ...
   
Google Books
Half-hours in Japan
By Herbert Moore
London, UK: Bradbury, Agnew, & Co.
1900
Pg. 97:
Then there are “dango.” You will read about Momotaro later on, and see how useful his “dango were to him. They are cakes made round, of millet-dough, with or without bean pulp in the centre. When there is a full moon, the Japanese take evening walks to enjoy the sight of it: and every here and there you pass a man crying, “Tsukimi dango!” “Millet cakes for looking at the moon!” They are eaten warm at such times, and no doubt keep off chills from the night air.
 
2 December 1955, Honolulu (HI) Advertiser, “Varied Items Displayed At Church Bazaar,” pg. A8, col. 4:
FOOD CONNOISSEURS will be interested in the chutney, jams, jellies, preserves, pastries, Japanese dango, (a sweetmeat made of mochi rice with “an” otherwise known as black sugar locally), and sushi either to take home or sample on the spot.
 
10 August 1964, Honolulu (HI) Star-Bulletin, “Japan Consular Event To Honor the Iturbis,” pg. 8, col. 2:
Among the delicacies which will be served at the coffee are dango, a Japanese pastry made of special bean paste and mochi rice; ...
   
27 August 1972, The Sunday Star-Bulletin & Advertiser (Honolulu, HI), pg. A-1B, col. 2 ad:
OVEN FRESH JAPANESE & CHINESE CONFECTIONERY
AMAKARA DANGO 1.19
(Shirokiya store at Ala Moana Center.—ed.)
 
7 April 1976, Honolulu (HI) Star-Bulletin, pg. E-8, col. 1 ad:
OIWAKE DANGO’S
DANGO DUMPLINGS ON SKEWERS
By TOSHIO SORIMACHI and YOSHIMASA SHIBASAKI
Two-Color Dango (Dessert)
Tri-Color Dango (Dessert)
(Shirokiya store at Ala Moana Center.—ed.)
     
24 August 1977, Honolulu (HI) Star-Bulletin, pg. D-8, col. 1 ad:
Tokoyo Shokuyin’s
RUSTIC STYLE JAPANESE CONFECTIONARIES
Prepared by Chefs from our Tokyo Kitchen
ANKORO DANGO on Skewers
AMAKARA DANGO on Skewers
NORI DANGO
(Shirokiya store.—ed.)
       
9 March 1978, Honolulu (HI) Star-Bulletin, pg. B-6, col. 1 ad:
OIWAKE DANGO
Tri-colored Dango, Yaki Dango and Amakara Dango on skewers.
(...)
OIWAKI’S
“Dango Dumplings”
(Shirokiya store.—ed.)
 
13 April 1983, Seattle (WA) Times, pg. E3, col. 1 ad:
Dango—small mochigome ball (confection) on skewer
(Uwajimaya stores.—ed.)
     
9 March 1999, Detroit (MI) Free Press, “News About Dango Fever,” pg. A5:
It evidently sounds great in Japan, where that’s the story of “Three Dango Brothers,” the latest music craze. About 2.5 million CDs of the song, which first appeared on television in January, sold out within days of going on sale last week. It’s expected to top the nation’s hit charts when new rankings are published today.
 
And sales of dango—rice flour formed into balls, steamed, toasted and served with sweet sauces—is booming.
     
Japan With Kids
“Dango San Kyodai” (The Three Brothers Dango) [28 April 1999]
Researched by Cornelia
(...)
Lyrics (with rough English translation):
 
1. Kushi ni sasate dango dango
mitsu narande dango dango
shoyu nurarete dango dango
dango san kyodai
 
Sticky rice paste balls
Three of them in a row
Dipped in a soy based sauce
The three brothers Dango
 
Google Books
Look Japan
Volume 45, Issues 517-528
1999
Pg. 3:
Sweet or savory, Japanese love their dango. And now more than ever! A song about the popular snack has taken the country by storm. “Dango san kyodai” likens three sweet dumplings on a stick to three (san) brothers (kyodai).
 
Serious Eats
August 13, 2013
Gallery: Snapshots from Tokyo: Eight Japanese Sweets Worth Savoring
JAY FRIEDMAN
Dango
One of the most traditional of Japanese sweets is dango, a dumpling made from mochiko (rice flour) that pairs well with green tea. Close to Isetan department store in Shinjuku is Oiwake Dango Honpo, historically known for its dango. (Honpo means the original store.) For 530 yen (just over $5), you get tea and a choice of two skewers of dango. I chose one with sweet soy that gives a syrupy, savory flavor not unlike the thick teriyaki glaze you’ll find in the United States. The other is topped with matcha (green tea) paste. The set comes with kombu (kelp) strips to break up the sweet flavors.
Oiwake Dango Honpo: 3-1-22 Shinjuku, Shinjuku-ku, Tokyo 160-0022 (map); 03-3351-0101; oiwakedango.co.jp
 
YouTube
How to Make Dango - Andango & Hanami Recipe
emmymadeinjapan
Published on Feb 26, 2015
Dango, dango, dango!  Learn how to make dango, a chewy Japanese confection on this Emmymade How to on Emmymade in Japan.
 
YouTube
Hanami Dango Recipe - Japanese Cooking 101
JapaneseCooking101
Published on Apr 1, 2016
This video will show you how to make Hanami Dango, a Japanese sweet Mochi dessert.
 
YouTube
Mitarashi Dango Recipe Japanese Cooking 101
JapaneseCooking101
Published on Nov 7, 2016
This video will show you how to make Mitarashi Dango, small round Mochi balls skewed on bamboo sticks and covered with a gooey sweet and salty brown sauce.
 
Insider
29 foods you need to try if you visit Japan
Tiana Attride Jan. 16, 2019, 4:31 PM
(...)
Dango is easy to eat on the go.
Dango are chewy steamed dumplings made of rice flour, often served on a skewer. They come dipped in sweet sauce or bean paste.