Headcanon: Bruce Wayne has severe baby fever. The kids claim it's an illness at this point.
The man has, what, seven legally adopted kids? There are more that he's not able to adopt due to certain circumstances.
It started with Dick. At first, he really, really dreaded the thought of being in-charge of a traumatized child once the adrenaline of rescuing the kid from the death of his parents subsided and he's faced with the reality that he now has a kid under his roof.
But Dick was such a cute kid, sure he's a little traumatized and had the temperament of a hurricane, but Bruce was really endeared by him.
It only got worse with Jason. The kid was so quiet, so shy, and so, so nerdy! Bruce reminded him of himself when he was still young and he and his little Jaylad would bond over books. Bruce even started going to theatres again thanks to Jason. The three of them would go watch movies or plays, and while Dick fell asleep during them, Bruce and Jason were starry-eyed and would whisper comments to one another, saying how this play didn't do this scene right, or that they completely wrecked the book.
Then came Tim. Bruce got Tim when he was much younger than Dick and Jason. He was still grieving Jason, but he tried to get it together for this kid's sake. By this point in his life, Bruce had grown a genuine fondness for children. He's the go-to member of the JL whenever a child is involved in the aftermath and they need someone to take care of the kid. Minutes later, despite the traumatic event the kid has faced, they're suddenly laughing, giggling, and riding the Bat's shoulders with their hands on the pointy thingies on Batman's cowl, “controlling” like that scene in Ratatouille.
As Bruce Wayne, he has set up numerous foundations that gave support to foster children and set up a system to sift through foster parents. The foundation also gives the foster parents allowance for the children that they foster. He also set up orphanages that he visits every weekend, and every kid who's gone through the foster care system and/or are living in the orphanages he set up, all have scholarships from Wayne Enterprises.
Knowing all of this as Batman's #1 fan stalker, when Bruce was at his lowest after Jason's death and having just legally adopted Tim, Tim decided to give him a gift. When Bruce opened the gift, he realized it was Tim's baby album. He never had Dick and Jason's childhood albums, so he never really saw them as babies.
This became the start of Bruce's baby fever. If then he just had love and sympathy for toddlers/children, now he wanted babies. He would fuss over at how cute Tim was when he was a baby, those fat, rosy cheeks, big blue eyes. Now whenever Bruce looks at Tim and Tim is particularly feeling the need for his father's affections (Tim is his father's son. I will never make an AU or headcanon where Tim doesn't love being Bruce's kid.), Tim would just give Bruce his best pout and flash him his blue eyes and Bruce would immediately fawn over him.
Then came Duke, Bruce was more careful with Duke, giving him a bit more space—because while he is Duke's guardian, the experience of Duke losing his parents to the Joker's venom was still quite fresh. Nonetheless, Bruce and Duke actually got on pretty well and enjoyed having a much “calmer” kid much like Jason and Tim feeling pretty jealous for a while.
Though Dick and Jason didn't have much in common when Jason was still robin, the two got along pretty well. So as an only child, this was Bruce's first time witnessing “sibling rivalry” and at first, he genuinely thought that Tim and Duke hated each other, but as he spent more time observing rather than intervening with their squabbles, he began noticing how Duke would put a blanket over Tim whenever he fell asleep on the batcomputer and Bruce came over to carry Tim back to his bed, or how he would catch Tim making Duke's tea whenever he woke before everyone else. It was the little things like that that made Bruce envious that he didn't have any siblings and made him want more kids.
Then he meets Cass, the first girl he's ever adopted, and he's just, like, awestruck. He's never had a daughter before, so safe to say she's definitely more spoiled. A simple "Bruce I want this, that, oh and those!" And she'd immediately have them. She definitely had Bruce wrapped around her fingers for a while. Not one of the Batsons could argue with Bruce for spoiling her—hell, they spoil her too. She's their only sister after all.
Cass definitely gets away with a lot of the shit she's pulled—but she's also the one who understands Bruce's struggles the most. Sure, Tim is Batman's #1 fan and knows all that Bruce has had to face, but Cass understands just how difficult it has been for him. Tim and Cass are similar in the way that they both love and appreciate Bruce.
Then when Damian comes into the picture, Damian, knowing that his father is the fearsome Dark Knight, experiences whiplash after the initial meeting and he begins to live in Wayne Manor. Bruce is fussing over him nonstop. He's so small, so cute, omg he has Talia's pretty green eyes, but he looks so much like Bruce! Is this what Bruce looked like when he was a kid? Damian is just so confused but begrudgingly accepts it. He's Bruce Wayne's only blood son, after all.
Bruce still grieves the fact that Damian doesn't have baby pictures and that the LoA never bothered to take such pictures. How could they! Damian's already 10 and he's still so cute! What more if he was a baby??
By this point, after 7 legal kids and more illegal kids, he woes the fact that he's never actually had a baby. Never had the joy of experiencing raising one. He dated Selina Kyle, but unfortunately they didn't share the same enthusiasm for having kids.
Now, whenever he's out in public and people start clamouring over him, the moment a parent shows him their baby, Bruce is immediately carrying it, cooing over it, kissing its head—reporters wouldn't be able to pull him aside for an interview because he'd just be so fascinated by the baby he's carrying.
His kids would have to physically pry away the baby and bring it back to the parents and Bruce would be all sulky and sad and Gothamites see this and are heartbroken for their precious prince.
#Make Bruce Wayne a Daddy is trending on Twitter, with many retweeting saying they'd be honoured to be his baby mama, but in classic Bruce fashion after he breaks up with Selina, he shares that news article about how scientists found a way for men to have babies without needing a woman. It was purely for petty reasons, but Bruce tweets somewhere along the lines: "How can I help fund this research further?" Or something and social media just explodes.
So do his children. Jason and Steph are laughing their asses off, Dick isn't sure how to react, Tim and Damian are horrified, Cass is supportive? Duke is concerned.
Thus, #Make Bruce Wayne a Mommy starts trending no. 2, just after #Make Bruce Wayne a Daddy.
