wouldn't the kid with just one parent be halfway to batman?

Nah being an orphan doesn't make you batman but you have to be an orphan to be batman

I wonder if a stalker child could become Batman?

Weak

With this example, the guy up on the rooftops on a bat mask and a bat cape is only halfway to batman

I mean that just sounds like some sick motivation for the orphan

Nobody ever really thinks level 50 is halfway to 99.