Typically having been written before Existence, the Mulder-Scully post-Requiem babies in these stories are not named William. And sometimes they're girls.

An Acceptable Level Of Happiness by Jenna Tooms

Ad Astra per Aspera by Charlotte Unsworth

Adopted Son by Kel

Amanda series by Mary Kleinsmith

And I Drove Away by Becka F.

"...and a Million Years Gone By" by DScully141

Another Gray Morning series by ML

As Circumstances Allow by Ophelia

Baby Girl Window by Becka F.

Bed of Lies by Baby Blue1

Bethlehem, Pennsylvania by Dramaphile

Birth by Teetee

Bittersweet Renaissance by Caroline

Breath In, Breath Out by little Starbuck*

Burning on Re-entry by bugs

Butterfly Kiss by Diana Rubenstein

the Changed series by Cathey Scully

Christopher Ryan Scully series by Jori

Closer by BioGirl

Code Adam by Julie Cantrell

Dark Seed by Bugs

Deep Breath by Catherine M.

Delivery at the Corner of Dupont and Connecticut by Rachel Wilder

Everlasting Miracle by DScully141

Fantasty in X Major by Ophelia

First Born by diamondlife17

Five Twinkies, an Alien Baby, and Chris Carter by mysterygirl1

Goodbyes/Hellos series by Donna

Great Expectations by bellefleur and Emily Sims

Happily Ever After by XfileySR

Having My Alien Baby by Alelou's Evil Twin

Home to Stay by Muldersangel

It's the Most Wonderful Time of the Year by Texas Rose

Joy Begets Sorrow by Parrotfish

Lamb by LostInOblivion

Maggie's Tips for an Unforgettable Baby Shower by Kel and Scetti

The Man to His Left by Jeri (Anna)

Maya by Diana R.

Mulder, It's Time! by Mulderache

The Night We Never Met by Heidi P.

Nova by Angel

On Angels from Heaven by Sandee

Progenesis by T Bishop

Sacrificed Futures by Nerys

Second Coming by RocketMan

Shoulders by Missy J

Stay With Me Always by Scully's Baby Blues

Survivors by lil gusty

Take My Breath Away by Ayla

To Breathe Again by Maddict

Unspoken by Megan C

Vulpecula by Jeri

Where You Are by LoveFox42

X Is For Xenogenic by Donnilee

Xenophobia by Donnilee

The Nursery Files