* Lucie Arnaz played the role of "Little Ricky" during the final season of the show. She appeared in the famous episode "Lucy Tells the Truth" where she is kidnapped and her parents are devastated.
* Desi Arnaz Jr. also made a few appearances as a baby, but primarily as a stand-in for his older sister Lucie.
It was quite common for children of famous actors to appear on their parents' shows, and both Lucie and Desi Jr. went on to have successful careers in show business, though in different ways.