Now that I have overheard it in the cubicle maze, I feel safe to make a gross generalization.
Having two children is no harder than having one.
I thought this may only have been true among my glorious pro-life friends but I felt safer to make the claim now that I heard it from the public at large. As a general rule, I assumed that all of my co-workers have the general worldview, so if we both agreed to the above proposition, it must have been correct.
Jen and I have discovered that the adjustment to the first child was tremendous in comparison to the second child. The two problems were organizing our house and organizing our heads. Our house needed to be drastically reorganized when Maria was born so that we had room for the changing table, diapers, stroller, playpen, co-sleeper, high chair, and 3 cubic tons of toys. Although we prepared tremendously for childbirth, we had prepared less for childrearing so we had many discussions about co-sleeping, vaccines, scheduling, introduction of solids, breastfeeding, growth curves, and poop color (my personal favorite). Once all this organization had occurred, it was easy to add Amelia to the family. She only required a bit of extra time since our house and heads were organized well. We had the tools and the plans already available, we only needed to act on them.
Of course, we also have a 2 year old "big helper" to help us with things like throwing away diapers and putting away toys. It's amazing how relaxing a minute can be when your littlest one is content in a new diaper and your oldest is occupied by trying to open a diaper pail.