A female child is called a girl and a male child is a boy (though a small percentage of humans are intersexual). Apart from the genitals, young children do not differ much by sex. Whether cultural and parental practices emphasize or weaken gender identity is subject to debate. For instance, parents often discipline boys more, which potentially weakens their inborn more aggresive nature making them more similar to girls. In general, the extent to which gender identity is formed during childhood or congenital is a matter of much debate within psychology and genetics.
In law, a person who is not yet a legal adult is known as a minor (known in some places as an infant or juvenile). For example, in many countries a person under the age of 18 is a minor. Most countries give additional legal protection to minors, and all countries except the United States and Somalia have ratified the United Nations Convention on the Rights of the Child.
Child development is the study or examination of processes and mechanisms that operate during the physical and mental development of an infant into an adult.
Pediatrics is the branch of medicine relating to the care of children. It encompasses ages from prenatal to teenagers and even young adults.
Stages of development include:
A street child is a child that lives on the street, in particular one that is not taken care of by parents or other adults, and also sleeps on the street because he or she does not have a home.  (http://www.enfants-des-rues.com/pages/html/uk/enfants_plus)
Both the psychological and economic fields share a special concern with education and language fluency including literacy and numeracy[?], and with identification and development of more unique talents into the economic variable known as individual capital.
Earlier branches of economics see humans in terms of labour for production[?], means of persuasion or protection, which tend to be skills acquired only in adolescence and adulthood. The human development view is more evident in sports, music and other performing arts, such as acting where the child begins training often as early as three years of age.
While there are problems with such early "streaming", child murder, child abandonment, military use of children and other major social ills are thought to be reduced by a human development approach - as as there is a high value assigned to children by the state.
The UN Human Development Index is a means of measuring well-being used to rank states by these criteria. Although child abuse is thought to be lower in countries with a high ranking on this Index, that is not easily proven.