A friend of mine just gave birth to her second child and were reflecting on how quickly we forget what newborns are like. They are like a completely different creature! Then I got to thinking about how once they get to be about 5 or 6 months old, they are this fun little cuteness machine.
It is as if you have a newborn for 3 or 4 months, it is replaced with a new creature called an "infant". Your infant then gets replaced with a toddler, then a preschooler, then an elementary school age child, then comes the age of puberty, a whole new creature called a "teen", then a young adult. Even the young adult is reborn when it becomes a parent.
Moms cry in mourning when that infant starts walking and rejoices in the birth of the toddler. Just as she cries when that preschooler dies the minute it steps onto the school bus for the first time and an elementart schooler is then born. I know that death sounds like a harsh way of describing it, but I feel it is fitting. Once that baby starts walking, there is no going back. You will never see that little baby again. There is no turning back. A new phase of life takes over.