The population of pre-school children in Ireland has increased by 17.9% since 2006, while the population of young adults has decreased by 12% over the same period.
Figures released by the Central Statistics Office, based on Census 2011, show the number of pre-school children aged 0-4 in the State is at 356,329.
The figures also show the population of young adults aged 19-24 stands at 354,313.
This is primarily a combined effect of lower births in the late 1980s compared with earlier years, along with the effects of migration among this age group.
The population of secondary school children, aged 13-18, has remained almost static over the past five years increasing by less than 1% to stand at 344,931 in April 2011.
Census 2011 figures also show an increasing trend for people aged 25-64 to live in rented accommodation over the past decade, with over 675,000 people in this age group renting, up by 51.4% since 2006.
The population of people aged 65 or over has increased by 14.4%, while the number of people aged 100 or over was recorded as 389 - an increase of 100 on 2006.
The average age of the population as a whole has increased by half-a-year to 36.1 years since 2006.
The rural population was older than in urban areas by almost two years.
All counties had older rural populations with the exception of Co Monaghan, where the urban population was more than half-a-year older than in rural areas.