When astronomy, biology, and culture converge: children's conceptions about birthdays.

The authors investigated the development of children's understanding of birthdays using structured interviews of 102 Israeli children aged 4 to 9 years. To fully comprehend the concept of birthday, children must grasp the relationship between the social occasion (the birthday party), irreversible biological growth, and the cyclical nature of the calendar. The authors' findings affirmed that a child's early conception is wholly social and self-contained (birthday parties confer a new age) and that young children believe that age can be affected by multiplying or skipping birthdays. The mature conception is socially based, but it is integrated with additional conceptual subsystems: the irreversible and independent unfolding of biological growth and the cyclical aspect of time. This enables the child to go beyond a magical approach to birthday rituals.