Photographing a newborn, or baby who has yet learned to crawl offers the advantage of posing them and knowing that they won't move when you click the shutter. Of course they will look at the camera and smile when you ask, just like when you ask them to sleep through the night because you are tired. They won't fuss while shopping at the grocery store, or while eating out at a restaurant.
Okay, by now you've caught on. Babies and toddlers seldom do what you want them to do. Parents can reflect back on the situation in different ways: 1) That went horrible, 2) That could have been worse, 3) That's just how it is with little ones. It's easy to focus on the what the majority of time was spent on (like waiting a long-time for food to be brought to your table at the restaurant while your toddler dumps out all the salt and pepper) instead of how the rest of the meal was incident free.
With a photography session this is even more evident. Photos are taken at fractions of a second. In the course of an hour session, if 120 photos were taken, that could represent less than actual second of time. So, that's the long way of saying that only moments are captured. 
My session with Will was really nothing to complain about. He was just a mover. There was a lot of placing him, then having him crawl away at top speed, then putting him back to the original position and repeating this over and over again. His mom, Kate, certainly kept busy and in the end stated "Did you get anything?". 
It's easy to think that if there's chaos and lack of control at all times, it's going to be tough to get good results. It's all about being ready, knowing what to expect, and patience that gets results. Or maybe it's jut acknowledging who's really the boss.
Who me?