When Dawnstar and Karate Kid arrive on the neighborhood streets of Washington DC, they observe a young couple walking their dog. The couple resemble "Marvin White" and "Wendy Harris" and their gray bulldog resembles "Wonder Dog" from the The Superfriends (1973).
While he may have been part of the similar "Super Friends" group (along with the featured Superman, Batman, Wonder Woman and Aquaman), no "Robin" has ever served on the "Justice League" in any of the incarnations. The closest they ever came to it was when Dick Grayson, the first Robin, became part of the Justice League when he took over as "Batman" after Bruce Wayne's apparent death.
The Characters "Dawnstar" and "Karate Kid" from the Legion of Superheroes were added for more ethnic diversity. Their costume designs are reminiscent of "Samurai" and "Apache Chief" from the Super Friends cartoon.
The Wonder Twins, "Zan and Jayna" were intended to have Cameo appearances at the Future Museum, but were removed.
Dante Basco, who voices "Karate Kid", and Jack De Sena, who voices "Robin", have worked together previously on "Avatar: The Last Airbender" with Basco voicing "Prince Zuko" and De Sena voicing "Sokka". (Coincidentally, 'Avatar' also involves a bald character trapped in a block of ice.)