A family's socioeconomic situation will have a major influence on a child's development. Children who have a strong attachment with their parents will generally feel more confident about themselves. They will not be constantly engaging themselves in daring tasks in a desperate attempt to seek approval from the parent. The financial situation will allow for children to have a more comfortable life. They will be able to get the toys they want or go to fun places. They will have shelter, food, etc and will not have to think about how to survive on a daily basis. The child's environment and the people around him will also provide influences. Those that grow up in a dangerous neighborhood might act tougher in order to protect themselves. Those that hang around troublemakers will tend to have more a troublemaker will as opposed to hanging around more obedient or caring kids.
Studies did show that the proportion of children showing secure attachment is lower in lower-income families. If the studies cited did not control for socioeconomic background, it is quite plausible that this is the 3rd factor affecting both attachment as an infant and later social development.
