Danny is adoption bait for more than just Bruce Wayne.
Idea #2
Warning! I use a translator, English is not my native language.
Danny is usually adopted by a living member of the Wayne family (whether adopted, biological, or otherwise). Now let's remember that there are Batman's famous parents, Martha and Thomas Wayne, who died tragically.
...And then there's Mary and John. And then there's Catherine Todd. And they're all ghosts who became one ghostly family because they love their living children. (Janet and Jack Drake go to hell)
They all live in a ghostly version of Gotham, in Wayne Manor, and sometimes haunt their living family members. How? Either through some kind of mirror, as this is often a link to the world of the dead, or they themselves, but in the form of shadows, invisible to humans.
They are happy to watch and know that their family is growing and is more or less healthy and happy, despite the difficulties. And it seems that in life, that is, after death, there is enough of everything.
But then he appears. A ghost-baby who left this world only recently. He died less than a year ago, and he still has no guardians or family on this side! Their Wayne-Grayson-Todd family needs to change that urgently. (Or, briefly, how Bruce and the kids got the adoption gene.)
That's how Danny got Mama (Martha), Papa (Thomas), Tati (John), Jaja (Mary), and Ma (Katherine). (I can't vouch for the parental names, as I just Googled them or remembered them from fics.)
That's how our sweet young ghost learned how crazy Gothamites can be… And he started following their example.
Sam: Damn, how do I open this?! * tries to open the can *
Danny: Here, take this knife * pulls a folding knife out of his pocket *
Sam: .... Why do you have a knife in your pocket?
Danny: My Ma said you never know when you might need it.
Tucker: Maybe you have a sharpening tool?
Danny: Yep * pulled out a sharpening knife from another pocket *
Sam: WHY DO YOU NEED SHARPENING?!
Danny: What if I get robbed?! Papa said you never know what can happen in Gotham!
Tucker: Dude, we're not in Gotham....
Danny:... I still need it.
And this is just the beginning! Gotham's madness is contagious! And now he has three parents from Gotham, and the other two are from the circus, and you never know what can happen in the circus!
And when he finished school and went to study in Gotham, able to create a portal to visit his parents, and also having a mirror for conversations, he meets and sees the Waynes. And at that moment, he has only one question.
Danny: Wait, if I was adopted by the ghosts of Bruce Wayne's parents, Dick Grayson and Jason Todd, then which one of them is my brother? And if they're all my brothers, does that mean the rest of my family are my nephews? But if I'm only Bruce's brother, then are Dick Grayson and Jason Todd my nephews too? ... Or does that mean I'm Bruce Wayne's brother, and also Dick Grayson and Jason Todd's brother/nephew, and also an uncle to the rest of Bruce Wayne's children...
Some random person nearby: 😶
Danny:… I think I'll save that for when they want to meet me, but for now I'll call Ma and ask her about that pie recipe. * pulled out a pocket mirror *
Babs: *heard everything through the camera* what was in that kiosk?
Tim: *also listened to everything through headphones* I don't know, but I want to too
