Uhlenberg, Peter (2000). Integration of Old and Young. Gerontologist, 40(3)
The ratio of children to old people in the population has changed dramatically over the 20th century. In 1900 the ratio of children under age 18 to adults over age 65 was 10:1; by the end of the century the ratio was 2:1. Around 2030, when baby boom cohorts have entered old age, it is expected that the number of children will about equal the number of old people (a ratio of 1.2:1). This convergence of the size of the two most disparate age groups in the population greatly increases the potential volume of contact that children have with old people as they age from birth to adulthood. If the social structures that connect old people and children did not change over the century, we would expect the amount of time that individuals spend during childhood interacting with old people to increase many-fold.