Martha suggests the names Christopher, Kevin, and Kirk. 'Christopher' and 'Kirk' refer to famous live-action Superman actors; Christopher Reeve who played Superman in Superman (1978) plus all of its sequels and Kirk Alyn who was the first actor to portray Superman onscreen and did so in Superman (1948). 'Kevin' actually refers to voice actor Kevin Conroy who became famous for voicing fellow DC Comics hero Batman in Batman: The Animated Series (1992) which was made by the same creative team as this series.
Here it establishes that in this continuity, Bruce Wayne became Batman before Clark Kent went public as Superman. In most other continuities, Kent's emergence as Superman predates Wayne's emergence as the Batman since Action Comics#1 came out before Detective Comics#27 (the respective first appearances of Superman and The Batman). The Earth-1 Kent began his career as a champion as a boy as Superboy well before the Earth-1 Wayne became the Batman. However, two stories indicate that the Earth-2 Batman was active as early as 1937 (Detective Comics#65 and World's Finest Comics#60); since the first Batman story in Detective Comics#27 was not an origin story, this may indicate that the Earth-2 Batman began as an adventurer before the Earth-2 Kent became Superman.