A rise in family income, represented in Figure 6.9 by the parallel outward shift of the budget line from ab to a b , enables the household to attain a higher level of satisfaction (point h on curve I4) by consuming more of both commodities and children that is, if children, like most commodities, are assumed to be normal goods (demand for them rises with income), an important if in lowincome countries where children are often in demand primarily as a source of future financial security. Note that as income rises, parents may spend more on each child, preferring a smaller number of children, each of higher “quality,” for example, healthier and better educated.