Since we weren't given a backstory of Constance's 4th child, here's my version.
(Warning bad edit ahead)

**

Adelaide Langdon

Tate Langdon

Hugo Langdon

And Constance Langdon

***

June 1979

"How do you think they'll react, darling?"

"Oh I think they might be happy!" Constance asked fidgeting with her hands.

"I don't think Tate will mind."

"You don't think Addy will be happy?"

"She wasn't happy when we brought Tate home from the hospital."

"Oh she'll get over it!" Constance rolled her eyes.

"What about Beau?"

"What about him, Hugo?"

"Do you think he'll be happy about the baby?"

"You know he doesn't understand anything!"

"Well calm down, hun."

"Can we just tell them already?" Constance said in annoyance.

"Sure." Hugo sighed.

Constance Langdon always dreamed of having the most perfect, beautiful little family.
But looking at her three children, she was beginning the think her womb was cursed.
Constance currently has three children and one on the way.
Tate, he had horrible behavior problems. Taking him out in public was impossible. He'd make sure to make his parents lives hell. As for Adelaide and Beauregard.. well they had other problems.

Now that Constance was pregnant for the fourth time, she was praying for the perfect child this time around. From the looks to the sweet angel personality.

She knew this one was her one perfect baby.

**

"Addy!  Tate!  Come sit down with mommy and daddy!"

"NO!" Tate threw his toy car at his mother.

"Cut it out, Tate." Hugo gave him a stern look.

"Oh he's only two, don't be too mad at him, daddy." Constance smiled and picked her baby boy up.

She then made her way to the couch and sat him down on her lap.

"Adelaide, come on!" Constance raises her voice.

"Play time!" Adelaide exclaimed.

"No Addy, not play time.  Come sit with us." Hugo says.

"Daddy!" Adelaide ran into her father's arms.

"Daddy!  Daddy!"

"What, Addy?"

"I six now!"

"I know that, silly." Hugo chuckled.

"Yeah and-"

"Alright enough, Adelaide!  Listen to me you guys.  I have a surprise for you!"

"Mama!" Tate arched his back, reaching up to pull his mother's hair.

"Tate, stop it!"

"Play time!" Adelaide attempts to break free from her father.

"Will you kids listen?!"

"What mommy?" Adelaide asks.

Constance smiles. "Mommy is going to have a baby."

Adelaide's smile quickly fades.

"You're gonna have a baby brother or sister you guys!" Hugo smiled.

"NOOOO!"

"Adelaide, stop that!" Constance shouts.

"Wha?" Tate looks up to his mother with a puzzled face.

"Mommy has a baby in her tummy!" Constance smiled and patted her stomach.

"Huh?" Tate looks down at his mother's hand over her stomach.

He then fuses and begins banging his fist on her barely there bump.

"Tate!  No!  We have to be gentle and nice to the baby!"

"NOOOOO!" He screamed.

Now the two parents have two screaming and crying kids on their hands.

Constance looked at her husband and let out a sad sigh.

**

As time went on Constance knew it was time for a bigger home for their growing family.  The house just next door had recently became available, the couple loved it and quickly put an offer on the house.
After hearing the news that they got the house, Hugo and Constance quickly packed up.  This baby was coming soon so Constance wanted to get situated as soon as possible.

Adelaide wasn't a huge fan of the house. Crying every night, sleeping in her parents bedroom, screaming 'We're gonna die in here!' Until she wore herself out. It was all so exhausting. Especially on Constance.

It is now November.  The baby is just a few short weeks away from being here.

Constance laid out on the couch with her feet up, feeling the kicks coming from her womb.

"Mama!" Tate stumbled over.

"Yes baby?"

"Boom!  Boom!  Boom!"

"What is that?!" Constance quickly sits up.

"Gun!" Tate smiled proudly.

"No sir!  Did your dad give you that?!"

"Yeah!"

"Give it to me!"

"No MINE!"

"We're not allowed to play with guns.  It doesn't matter if it's not real, it's a big no no!"

Constance took the toy gun from him and marched into her husbands den.

"What is this?" Constance slams it down on the desk.

"That's a toy, darling."

"I know what it is!  I thought I told you no toy guns!"

Hugo stares blankly at his heavily pregnant and very heated wife.

"..It's a toy."

"That is not the point, Hugo!  We teach him it's okay to play with it, he grows up and wants to play with real ones!"

"Heh!  It's not that serious, baby.  He's not going to turn into some type of killer because of the toys he plays with."

"Please just.. No more toy guns!"

"Fine." Hugo sighs.  He then grabs the gun and tosses it in the drawer before slamming it shut.

Constance then walked back into the living room to find the two children playing sweetly with each other.

A smile spread across her lips.  She walked over and kneeled down beside them.

"Hi mommy." Adelaide smiles.

"Hi, honey!"

"Play?" Tate smiles.

"Of course!  What are we playing?"

"Monsterrrr!" He knocks over Adelaide's doll house making her laugh hysterically.

"You find that funny, Addy?" Constance chuckled.

"Yeah!"

Tate then looked at his mother.  His eyes traveling down to her round mid section.

"Big!"

"Mommy is big, huh?"

"Yeah!" He throws himself into her stomach.

"Ouch!  Gently Tate, gently, honey."

"Mommy is the baby going to be a girl of a boy?" Adelaide asked.

"We won't know until it's born.  What do you want?  Would you like a little sister?" Constance smiled and twirled her black curls in her fingers.

"No!"

"Aw, why not?" Constance pouts.

"I don't want babies!"

"Well honey, that's not very nice.  You love your brothers, don't you?"

"Yes."

"Well you'll love this baby too."

Adelaide gave her mother a mean look.

"Don't make that face." Constance said with irritation in her voice.

Just then Tate placed his ear against his mother's stomach and smiled.

"Hi baby!" He said playfully hitting her belly with his hand.

"Aw!  Is the baby kicking you?"

"Yeah!" He laughs.

"Do you wanna feel, Addy?"

"No."

"Oh come on, Addy.  Be a nice girl!"

Adelaide gave her a look before slowly moving her hand to her stomach.

"Do you feel your sister?"

"You said you don't know what it is."

"Well I guess I'm just being hopeful.  I would love a beautiful baby girl with golden curls, and the most beautiful light blue eyes.." Constance says smiling softly.

Anger grew within Adelaide.  She yanked her hand away and left the room.

Constance sighed. "Do I have to get up now?  Okay, let's try this." She says struggling to get up off the ground.

"Addy!  Addy!  Adelaide!"

"No!  Go away!"

"Addy.. what's wrong?"

Adelaide turned to her mother in tears. "I wanna be a pretty girl!  You're gonna love the new baby more than me!"

"Honey, that's not true!" Constance took her hand.

"Go away!  I want my daddy!" Adelaide snatched it away and ran to her father.

Constance sighed and walked back to the living room.

**

December.

"Be good for Mrs. Davis.  When daddy and I come home, we'll have a brand new little baby!" Constance smiled, cupping both of her children's cheeks in her hands.

This time around Constance's labor was far more faster than her past three deliveries.

Her water broke in the kitchen, fancy dress and heels.  Her hair was perfect, and her makeup was done.  Constance always looked amazing no matter how uncomfortable she was.

Getting to the hospital, her doctor checked her.  She was dilated six centimeters already, and only four hours later it was time to start pushing.

"Push Constance! Harder, harder, harder!" Her doctor instructed.

Constance pushed as hard as she could before taking a deep breath and going at it again.

Hugo held his wife's hand and watched with wide eyes. Even though this is their fourth time doing this, it all still amazed him.

"AgAhhhh!" Constance's scream told him that the baby was on it's way.

She felt the ring of fire as the baby's head made it's way out.

"The baby's crowning. You're doing great, keep going!" Her doctor said.

Tears rolling down her cheeks, Constance pushed one last time and her baby was born.

"Oh my baby! What is it?" She asks.

"It's a girl, Mrs. Langdon!" The nurse says.

"Oh it's a baby girl!" Constance cried.

"Hugo look! She's perfect! Oh she's so perfect!"

"She looks like you, darling!"

"Yes, I know." Constance giggled.

"She's so beautiful. Yes you are! You're mommy's pretty girl!"

Soon the baby and her mother were cleaned off and sent to recovery.

Constance held her perfect little baby girl in her arms and took in every little detail.
She had never see a more beautiful baby.

"Honey, we did it! Look at her.." Constance held her tiny hand and smiled, staring deep into her light blue eyes.

"She's the most gorgeous thing I've ever laid my eyes on."

"She is pretty cute, huh?" Hugo chuckled.

"Yes.." Constance smiles softly. "Honey, I want to name her Rose.. because roses are beautiful.. just like her."

"I think that's a beautiful name, sweetheart." Hugo kisses the top of his wife's head.

"You've got my nose." Constance scrunches her nose and giggles a bit.

"And look! Golden hair just like mommy.. you're my little mini me, aren't you?"

The baby coos and Constance's smile grows.

"Oh goodness, my heart..
My beautiful little beauty queen."