In Portugal, for over thirty years, fertility has fallen below the level required to replace the current generations of parents, which is well reflected in the continuous decreasing of younger people.
The present article begins with a note on the diversity of Children and Adolescents concepts, and then focus on the evolution of the number of “Children and Adolescents” resident in Portugal, highlighting the contribution of demographic variables to the past, present and future dimension and structure of this population group and analysing phenomena such as parenthood, reproductive health, mortality and educational level.
The first challenge was to unambiguously define the object of analysis, due to the thin border between children and adolescents and the difficulty in inserting them in the usual functional groups adopted in demographic manuals. Even within the same category there is no international consensus on the age limits to use, as the concepts differ according to the laws of each country and even in
a given country they follow the societal evolution.
Due to the difficulties in finding an accurate and consensual definition, we created a broader group named “Children and Adolescents”, which encompasses the persons aged under twenty years and follows the standard demographic criterion that considers children as 0-14 years and adolescents as 15-19 years old. However, to facilitate comparisons, we decided to include the following
 ategories: under 15 years (disaggregated in individuals aged under three years;
from 3 to 5 years and from 6 to 14 years old); under 16 years; under 18 years; under 19 years old. The number of effectives under twenty years old was reduced in 50 years, between the 1960 and the 2011 censuses by 1.2 million people of individuals.
This population group is expected to decrease by about 2 million persons between 1960 and 2060.

Keywords: Children, Adolescents, Live births, Abortion, Cohabitation, Mortality, Level of Education