Oh gods, I am certain that piles of people smarter than me have covered this one, lol! Isn’t there a whole twitter world that built them a sparkly future?
But since you asked…
They get married during the first Santos term, and Donna is pregnant with their first daughter before the second one ends (it’s my headcanon, so of course he wins re-election). Therefore, post-administration they’ve got an incredibly independent toddler on their hands, and a second baby girl shortly after.
Surprising everybody but Toby, Josh takes over more of the childcare and becomes obsessed with exposing the girls to museums and dance lessons and every bonding activity he can think of–lots of hair braiding and nail painting and embarrassing photos that Donna holds for blackmail as needed.
Donna uses her clout as former FLOTUS COS to push for pet causes like criminal justice reform, and eventually reunites with CJ to co-found an NGO that tackles a wide range of progressive issues using the tactics CJ honed working with Franklin Hollis. Zoey Bartlet joins their staff, and becomes their daughter’s favorite babysitter–she even teaches them self-defense moves she learned post-abduction, making the Lyman-Moss daughters the safest ones on the block.
When the girls are in their teens, Donna decides to re-enter politics, this time as a Congresswoman. Josh amuses the press by running bake sales and holding photo ops and being the political spouse with much better savvy than he used to hold press conferences.
Their eldest daughter graduates top of her class and heads straight for law school.
all the characters on the west wing are great but let’s be real the women blow all the men out of the water. cj cregg, press secretary of my soul, chief of my heart, badass feminist extraordinaire. donna moss my sun and moon, who grows into herself in the most heartbreaking way and turns into someone so strong and so sure of herself while still being caring sweet and kind. ainsley hayes had my heart the minute she slammed sam pretty-boy seaborn. abbey bartlet who holds her own all the mf time and refuses to be overshadowed by her husband. annabeth schott who is 4 feet 11 inches of star power and sass. u can have your Leo mcgarry and Sam seaborn and I’ll keep my ladies thank u and goodnight
do you ever think about how jed bartlet went “you know what because of Politics i can’t legally adopt you but to make it unofficially official here’s a family heirloom that i confirm is passed along from father to son for generations, and is already probably worth hundreds of thousands of dollars and now possibly millions since now i’m also the president and it was made for my family by paul revere. And sure I have 3 daughters but I already have a grandson and a son in law but ur my son now u get the carving knife here you go i love you happy thanksgiving give your sister CJ and your brothers Sam, Toby, and Josh a hug before you leave”