This article examines the relationship between household demographic pressure and interage transfers for a group of Maya subsistence agriculturists in Yucatán, Mexico. The authors use data from a field study conducted in 1992–93 on individual time allocation, relative productivity by age and sex, and caloric costs of activities to estimate age schedules of average consumption and production. Using these, they investigate the net costs of children to their parents and find that children have a negative net asset value up to the time they leave home. The direction of net wealth flows in this group is downward, from older to younger, and in economic terms the internal rate of return to children is highly negative up to the time they leave home. Nonetheless, children play a critically important role in the family's economic life cycle. On average, girls offset 76 percent of their consumption costs before leaving home at age 19, and boys offset 82 percent before leaving home at 22. Without the contributions from children as a group, parents would have to double or triple their work effort during part of the family life cycle if they were to raise the same number of children. By the thirteenth year of the family life cycle, children as a group produce more than half of what they consume in every year, and after the twentieth year children produce more than 80 percent of what they as a group consume. The authors also find that the elderly in the sample, ages 50 to 65, produce more than they consume. Thus while children have a negative net asset value to parents, the timing of their children's economic contribution across the family life cycle plays a key role in underwriting the cost of large families.