There are two classifications relating to the age of the youngest child in a family nucleus. They are:
The standard classification of age of youngest child is a flat classification with 51 single year categories ranging from one to 49 years plus a category for '50 years and over' and a category for 'less than one year'.
The standard classification of age of youngest dependent child (under 18) is a flat classification with 18 single year categories ranging from one to 17 years plus a category for 'less than one year'.