It would seem obvious to say that development does not stop at birth. In fact many systems (cardiovascular, respiratory, gastrointestinal, homeostasis) undergo significant changes at birth, and many others (neural) have not yet completed their development.
Postnatal development can be broadly divided into the age categories of: Neonatal Development (birth to 1 month), Infancy (1 month to 2 years), Childhood (2 years to puberty), Puberty (12 years to mid-teens), Young Adult a new category (late teens to early twenties).
As an introduction to postnatal health issues read NHMRC Publications list that relates to child health. Many factors causing abnormal development can also lead to childhood mortality.
In developed countries, we sometimes forget that every year (mainly in developing countries) some 12 million children die before reaching their fifth birthday, many of them during their first year of life. Of these, 70% are killed by one of five causes (diarrhoea, pneumonia, measles, malaria or malnutrition) and often by some combination of them (WHO Fact Sheet N96 November 1995).
For more child population data look at the section below on Child Health Statistics of the world, between and within specific countries.
Note this current project focuses on prenatal development, so postnatal content is not as detailed.