Despite the apparent advantages of many children, it is not clear that, from a strictly economic point of view, parents gain. Children may end up costing more than parents expected; for households close to subsistence levels, food clothing and housing many children is a chief concern, and the need in some countries to provide girls with a dowry is an additional burden. Support in the parents' old age is not certain - some children will die and, of those who survive, daughters may move to another village with their husbands, while sons who move away to work may not prove as supportive as was hoped often because they face difficulties in obtaining reasonably paying jobs. Even when parents seem to gain from large families, children may lose. This is obviously true when births are closely spaced; the resulting harm to the health and nutrition of mothers can cause low birth weight, early weaning, and poor health of children in the critical early years. Older children may also be handicapped. Even in developed countries, studies show that children in large families and those born close together tend to be physically and intellectually inferior to other children.
Studies in France, the USA and the Netherlands have shown that a large number of children in a family has a negative effect on classroom performance and test scores.
The reason that parents in developing countries have more children than parents in the West is not because they do not have access to contraception. In most cases they do. Birth control has been widely available in the developing world, either free or at subsidized prices, for up to 40 years. The reason for the larger families is that third world cultures are more pronatalist that Western ones. They are based on very different assumptions about family life and the value of children, and these are reflected and reinforced in social values and laws related to marriage, divorce, inheritance, custody, taxation, social security, employment, education and pensions.