I am really struggling with this!! My two boys are ages 4 and 16 months. I would really like to have a third, but I have so many days still where I think I could not possibly add another to the mix. I know that you have to be really organized, have a routine down, etc., in order to maintain sanity amongst the chaos of 3. I know it is not easy. In addition, I have a very highly spirited first child, with very high needs that often tend to supersede everything else. I have a hard time juggling/balancing the needs of 2, and can't even imagine there being 3. I also have a hard time juggling our schedules/lives to keep things running smoothly. I am working almost full-time, and it is constantly a struggle. I feel like something would really have to change to make it work with 3.
Ideally, I would wait until my 16 month old is 4 or something, but I am running up against the impossibilities of fertility! I know, I could put it off, and just give it a wait and see approach, but I don't want fate to decide because I waited too long! (I will be hitting 40 in a couple of years) We had issues getting pregnant the first time. Plus, not sure I will still have all the energy required when I'm 41, even if I do have the physical capacity to sustain a pregnancy. So, that puts me at waiting until DS2 is 3 years old, which means a pregnancy at the end of this year. Yikes. It's just all so overwhelming.
So, how did this all work out for you? I have read numerous posts about the transition to 3, and it seems like it boils down to this: your experience will depend on the temperament of your children, which is determined completely randomly and is entirely unpredictable. Yeah, a lot of moms report the third is more easy going because he or she "has to be," but others have also said the third was the hardest (whether it be for developmental issues or just different temperament).