Overpopulation is a complex issue, as it can refer either to a global or regional problem of a population exceeding the carrying capacity of the land, or it can refer to local overcrowding.
One major effect it has in urban areas is a decline in air and water quality. Many cities in developing nations have vast slums with little access to clean water or modern sanitation. This can cause the spread of epidemic diseases and has a negative impact on health. In rural areas, overpopulation can result in overgrazing (the so-called "tragedy of the commons"), depleted water tables, and increasingly over-farmed and infertile land.
There are two different responses to this. While some people may have large families to increase potential income and increase the odds of children surviving to adulthood, a more common response is to limit childbearing. In wealthier nations, overpopulation may contribute to declining birth rates. In the developing world, limiting childbearing combined with a preference for male children can lead to gender-selective abortion and skewed gender ratios.
Overpopulation has economic and social impacts on families. When overpopulation occurs, this can lead to a surplus of workers, shortage of housing, and a possible shortage of supplies and materials. These will have a negative impact on families. An oversupply of workers means wages will drop. Families may have less income to spend. A shortage of housing and supplies means prices for these things will rise. This decreased income coupled with increased costs will negatively impact families.
Families may also be impacted socially. Overcrowding could lead to more disease and pollution. It could lead to increased class size in schools since there would likely be more kids. If income levels drop, it could lead to increased poverty. This may cause crime to rise. If both parents are working, kids may be left unsupervised at times. This could cause issues if the kids get into trouble. It may also lead to increased child-care costs if parents are working.