Here are their two adventures from so long ago!
The Sons Of Superman And Batman
Superman (as Clark Kent) married reporter Lois Lane, and Batman (as Bruce Wayne) married Kathy Kane (Batwoman).
The boys played together, yet young Kal would bully young Bruce with his super powers. This set Kathy against Lois, and could have separated the Superman and Batman partnership as well.
The Abominable Brats
It is years later, as seen by the grey in Clark, Bruce and Kathy's hair, and the sons have gotten older.
Earth-E would be a place where adventures of Superman and Batman in the late 1940s and 1950s took place (basically from after the tales of the Justice Society in All-Star Comics #57 in 1951 to just before the Justice League in Brave and the Bold #28 in 1960).
Superboy facing an adult Lex Luthor, Superman working for the Daily Star and then Planet, Batman's odder tales and even working with Batwoman), and be a bridge between Earth-1 and Earth-2. But, Mark went to work for Marvel, so it never happened...and, like the early stories is only imaginary.....