Never?Classically we speak of roleplaying games as allowing you to imagine you are a powerful wizard, mighty warrior, or checks notes dragonman mcdragonface. But how often do people use RPGs to explore the fantasy of having children, or alternatively being child free for a little while?
Other than Pendragon, where characters get married and have children they end up playing as characters when the parent inevitably die, I can't think of many games where that kind of thing is built in. In Cthulhu type games, like Trail of Cthulhu and Delta Green, players can select family members as their sources of Stability (something that helps keep them sane), but it doesn't have to be kids and who knows how involved they'll be in the game?But how often do people use RPGs to explore the fantasy of having children, or alternatively being child free for a little while?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.