I love playing as young adults! Children/teens not so much. Gotta keep the game going though!

Rather than making your sims have kids, you could just have a friend move in with them, so that you have someone to play when your sim dies. I've done that before, as I don't always feel like having to play the younger life stages and having to deal with school and homework and phases. In one of my saves, my sim went on vacation to Selvadorada. While there, she met two locals whom she quickly befriended. When she returned home, they both moved in with her and are helping her run her vet clinic.