Demon(bat) child
Okay quite honestly this could work with just about any one of them other than Damien but I was thinking it with you isn't yet again
what if he was the child of Talia and Bruce it doesn't necessarily have to be with Bruce but just talia and he was sent to Batman and the reason he stole the wheels off the Batmobile was so that he had an in with the Batman
if I'm being honest I really didn't have much more to that idea it just occurred to me but I guess
that would mean that he knew about Damien his entire teenage years whatever how old was Jason when Damien was born well I guess that depends off the timeline doesn't it i'm rambling anyways
which would also mean that Talia would probably Rampage for quite a while when Jason gets killed by the Joker cuz she wasn't able to protect her baby boy i like total imagine she would feel incredibly relieved when she spots her baby boy roaming the street because he's alive and she hasn't wait till I heal him now you know Whatever
yeah that's all I got sorry for any grammar mistakes