As a mom of 6, I can say that there's not really a set age to transition. It's more the consistency when you do make the switch. However, I was recently reading the sleep book "Healthy Sleep Habits, Happy Child," (which I highly recommend), and Dr. Weissbluth was saying that it actually might be better in your situation if you waited until after the baby is born, and had the baby sleep in a cradle or bassinet until at least 4 months, at which time your baby and your toddler will be basically adjusted to the baby's schedule and routine, and the transition will be smoother. The baby then moves to the crib and the older one graduates to a "big" bed. Or you could leave the crib empty for a couple months if the baby can still fit in cradle/bassinet, so it won't seem so abrupt and displacing for the older child. The reason he suggest this is that if you make the transition before baby is born, everyone's schedules get thrown off, and the toddler is often a little confused/insecure, which can throw off what you worked so hard to establish. Either way, though, as long as you are consistent, making the transition before baby or after will work out. Good luck, and congrats on your new baby.