The 5 days normal infant lifespan is hilariously bad

I play on Long. That gives you plenty of time. Now, that I've had several infants (not all at once) in my game, I no longer stress out about the milestones as I did in the beginning. In many ways, they occur without help, just as in RL. Take a deep breath and change the length setting in your game. The only time I played with aging off was back in Sims2 when we didn't have but the one choice. I really liked Epic in Sims3, but Long is a good substitute.