ROTTERDAM - That poverty is unhealthy has been clear for years. But researchers from the Erasmus School of Economics now discovered that poverty can have a developmental impact on children as young as four months. In poorer families, babies are more likely to be overweight, toddlers more often have a language delay, and teenagers are more likely to have mental health problems, the Rotterdam researchers found, the Volkskrant reports.

Researchers Coen van de Kraats and Bastian Ravesteijn studied data on the weight, language development, and psychological and social problems of about 153 thousand children born between 1998 and 2017. Studying this data set gave them "a better understanding of how early deprivation affects the course of a life," Van de Kraats said to the newspaper. "And then we can investigate how children's opportunities can be improved."

The researchers found that children from the richest families scored better on all fronts than children whose parents have low incomes. And the differences are visible from as early as 4 months of age. 

In babies, the differences are mainly seen in weight. "Basically, the higher the income, the smaller the chance that a child is relatively heavy, " Van de Kraats said. As the children get older, the differences in weight decrease slightly, but increase again from about 2 yeas of age. By age 14, one in 10 rich kids were overweight, compared to one in four among low income families. 

Language delays are also more common among poorer families. The data set included child health clinics' information on 2-year-olds that can make two-word sentences. Among the poorest families, 21 percent of 2-year-olds couldn't do this, compared to 6 percent in the richest families. The poorest children were also much more likely to have a doctor or nurse judge their language development as 'doubtful' or 'inadequate' - 41 percent compared to 11 percent of children in the richest families.

Kids who grow up in low-income homes are also more likely to struggle with their mental health. Children in the Netherlands are assessed for signs of mental health problems in group 2 and 7 of primary school, and class 2 of secondary schools. Parents, teachers and the child fill out the Strengths and Difficulties Questionnaire to help identify psychological and social problems. 

"Worrying scores are more common in the families with the lowest incomes," Van de Kraats said. By age 6, 5 percent of the richest kids and 18 percent of the poorest kids had a score that indicates a risk of mental health problems. These differences still exist by age 14.