I love generational games- that is to say, games in which enough time passes for pcs to have kids who themselves become the next generation of pcs.
My 5e campaign has featured a five-year downtime break. Before or during that period, a number of pcs had kids (including two pcs who got married and have had one, or 13, depending on how you count- there was some divine intervention shenanigans involved, resulting in 12 warforged 'children' coming to the two).
I actually have a "wooing" downtime activity written up for pcs who want to start families.
I've had pcs in my game have kids in 1e, 3e, and 5e so far.