My headcanons about the Hargreeves children:
Luther and Sloane would have had several children and tried to raise them responsibly and give them love. They wouldn't have had any specific plans for how many children they wanted, but they would have accepted anyone who came along.
Diego and Lila wouldn't have planned for three children, but they would have been a couple constantly working part-time jobs and traveling the country. They only had bad parenting examples, so Diego and Lila simply raised their children in a way that Reginald and the Handler certainly wouldn't have. So Gracie and the twins would have been rowdy kids who wouldn't have been restrained in their mischief. Diego and Lila would also be the kind of people who, upon hearing of a child's fight at school, would run to the school to find out whether they won or lost.
Allison most likely wouldn't have been ready to have a child with Raymond. She would still be worried about Claire and afraid that if there was another child, she might not be able to bear the loss of both. She would also feel guilty towards Claire for not being a good enough mother before.
Klaus and Dave could have adopted a child, probably a Vietnamese boy. And Dave would likely have been a better father than Klaus.
Five would have simply wanted many children and a large family. He would have gotten a dog while he searched for a suitable partner. Five would also often babysit his siblings' children, pretending to be a caring grandfather.
Bens and Jennifer would have had a daughter. Sparrow Ben would have insisted on a second child for some time, but Jennifer would have refused because she knew he wanted to split the children equally with Umbrella Ben. No one knows who the girl's father is.
Victor would have adopted Harlan, marrying Sissy, and would likely have supported her as he had before.
Marcus wouldn't even be ready for a relationship, so he didn't think about children until he sorted himself out and his fears of close interactions with people.
I think Fei could have adopted a child if she wanted, and it would have been a teenager, because she would have been afraid she might do something wrong raising small children.
Alphonso hasn't thought about children yet.
Jayme would have more cats than children, and perhaps would have shown the kittens to her siblings, calling them her children.
Christopher has decided he won't have children because he's not sure he's biologically capable of having them, and because he doesn't consider himself responsible enough for children.
I like some of these hcs: and also here's some of mine:
Klaus would likely have adopted a troubled teenager at some point and he's really good with troubled teenagers because he sees a lot of himself in those types of kids.
Phil can be very temperamental and a kid would definitely test that part of his brain that's like- "attack first, ask later". He likely would not want to have a kid because he's afraid that if he snaps he might hurt them.
Carla is surprisingly good with little kids, but like Allison would struggle with the temptation to end all her problems with her power because she can literally have the final word on anything if it's made into an argument.
Ryan would also be good with kids, until he accidentally gives one of the kids a power that nearly ends in several people dying. He babysits some of the kids, and is there for emotional support (also to keep the others from killing the kids with more of an additude)
Eudora is the parent who puts the rules into place and has to do the lectures because everytime she tries to get Diego and Lila to do them they're terrible at it.
Stanley would grow up with Grace and the twins, struggling with the fact that he's not "technically" their kid. He'd have to be reassured many times by many different people that he's still apart of the family. He would definitely be a bad influence to the younger kids.
Destiny and Jayme both want more cats than kids, but Jayme is a worse babysitter, one of the kids under her watch almost set the house on fire and another time she allowed one of the kids to drink beer. Destiny is more responsible, and has been the one to stop disasters from happening over and over again.
Raymond has an easier time getting Claire to talk to him about stuff and overall is the one who talks to Claire when she's starting to have a bit of an additude because Allison isn't going to risk another rumoring incident.
Umbrella Ben is basically a QPL friend to Jennifer and takes care of the kid that S!Ben and Jennifer had together, this ends about as well as you'd expect it considering he died as a kid and the only child he's been interacted with for a while is Klaus