4) Damian Wayne (Robin)
If you’re out of touch with Batman comics, it might surprise you to know that Bruce Wayne fairly recently found out that he had a son from Talia Al Ghul (half naturally born, half grown in a tube).
Damian is raised by Talia before being given to Bruce aged ten where he proves to be a spoiled and violent brat. However, he undergoes a dynamic change of heart over time and eventually becomes a worthy Robin. Although Damian generally works with Dick Grayson’s Batman, if translated to film he could team up with his dad, as there is a lot of dramatic possibility there.
A Batman film focused on a fractured father and son relationship could be brilliant. The movies often focus on Bruce’s daddy issues anyways, so it would interesting to see him address those by raising his own son.