Kintaro was the childhood name of Heian Period samurai Sakata no Kintoki, who was said to have defeated a bear in sumo wrestling as a child. Toy representations of Kintaro riding a bear have come to symbolize strong and healthy boys, and are often displayed on Children's Day, May 5 (formerly Boys' Day).
There is even a candy featuring the boy's face: Kintaro-ame. But being described as "Kintaro-ame-like" doesn't necessarily have a positive implication. Because the face on every cut end of Kintaro-ame is the same, the description can be used to mean someone who looks just the same as everyone else and has no distinct personal character.
The origin of Kintaro-ame is unclear. It is generally believed that the manufacturing technique was invented in the late Edo Period in the Kansai region. The motifs originally used were Okame (a funny-faced woman) and Fukusuke (a man with a big head), symbols of good fortune.