When do your sims have babies?

Usually as young adults but that's not a hard and fast rule. And if an older Sim wants to enjoy grandparenthood to the max, then there's always saving up enough points for a potion of youth.

My sims have babies as YA or adults depending on the story. But i prefer them to have babies when adults. This way they can 'live' a little before all that responsability.

That one thing I procrastinate the most! But if I wouldn't, I'd say probably several days before becoming fully responsible adults.

Young adult, of course - right after the usual wedding.

I usually have my sims use a potion of youth towards the end of their young adult phase so that I get two periods of young adulthood. The first one is primarily for career and getting established in life. The second young adult phase for finding love and getting married. They have kids towards the end of that second young adult phase, so that as an adult everything is established in terms of home and career and they can focus all of their energy on raising the kids.

Usually late in Young Adult stage or early in the Adult stage. But I've done right after becoming a young adult and relatively late in adult stage too (though that last wasn't exactly intentional. Fortunately, one parent had the long life aspiration, or I would have had an orphan kid.)

Rarely, to be honest, but if so as young adults, because as adults, they would become elders before their children even reached young adulthood which seems a bit too old to have children anyway.

Young adult and/or adult depending on the story. I usually play with ageing off though and manually age up my sims when I want to.

In early young adulthood.

Young adult. As soon as possible. Usually do the whole find a partner, get married, try for baby thing within the first sim day of playing. Not very patient when it comes to starting sim families. :D