Because their year is equal to 4 hours of our time, sometimes the ages get a bit strange looking. I've adopted kids that seemed to "catch up" in age to a child I had before they came and vice versa. I've also had a hubby that was a year older than his wife initially, become the same age as her, then revert back. It's the timing.
As far as the additional generations go, once you hit the button, each child is randomized similar to the way they are when you are selecting a new adoptee. This is so that you are not stuck with someone who is only 13 (for example) and unable to cook or work or someone who is nearly out of childbearing age or for whom proposals would be very slow in coming. Other characteristics are randomized as well: desire for children, occupation and level (beginner or novice.)
Yes, we are all hoping that the age at death is added with the next update.

Edit: I left out an important part. :P For the first two years of life, while the mother is carrying them in "nursing" mode, the child DOES age faster. They age two years in four hours while the others only age one.