Cho-Cho was a "health clown" who toured the USA during the 1920s, visiting classrooms, and trying to encourage kids to eat more vegetables, take baths, and brush their teeth. In a way, he was like the opposite of Ronald McDonald (Ronald being a clown who encourages children to eat junk food).
CHO stood for "Child Health Organization," which was the group that dreamed him up and sent him out. Some more info from the book Children’s Health Issues in Historical Perspective
The clown Cho-Cho was trained to "teach health, sugar coated with all the nonsense and fun of the sawdust ring." The Health Fairy, a public health nurse, told "delightful stories," and a cartoonist drew "a white loaf of bread into a sour-faced boy,... a brown loaf into a round-faced smiling boy," and "vegetables weeping great tears because children do not eat them."
All three travelled to elementary and secondary schools, as well as exhibitions, fairs, and "any place where children were gathered together. A less traditional figure was CHO's pseudo-professor Happy (played by Clifford Goldsmith), who entertained child and adult audiences with snappy health maxims.
Happy, the Health Fairy, and the cartoonist worked well within the boundaries of CHO's program, but when the clown who played Cho-Cho began to regard himself "as a real authority on diet, hygiene, and even the morals of childhood," and deviated from his "carefully learned lines," the organization had to find a new Cho-Cho.
Popular Science Monthly - Feb 1920