Deaths in children under five occur one and half times more often in England than in Sweden, a study has found.
If the child mortality rate was the same in England as in Sweden, more than 600 fewer children would have died a year in England during the 10-year period analysed, researchers said.
The UK has one of the highest child mortality rates in western Europe, and although the UK and Sweden have similar levels of economic development and healthcare, the UK's more unequal wealth distribution leads to poorer maternal health during pregnancy.
This causes more babies to be born prematurely and with a low birth weight, researchers from the UCL Great Ormond Street Institute of Child Health said.
Children born in England also tend to have more birth anomalies - such as congenital heart defects - than in Sweden.
The study, published in the Lancet, used medical data from the NHS and the Swedish health service to compare births from 2003 to 2012, and track the children's health and death records up to their fifth birthday.
These records included information on the mother's age, the family's socioeconomic position, length of pregnancy, the child's birth weight, gender and whether they had any birth anomalies.
Overall, the study included more than 3.9 million English births, with 11,392 deaths, and more than a million Swedish births and 1,927 deaths.
Between two days to four years old, the child mortality rate for England was one and a half times higher than for Sweden (29 deaths per 10,000 children in England, compared with 19 in Sweden).
If the child mortality rate was the same, 607 fewer child deaths per year would have occurred in England, equivalent to 6,073 in total from 2003 to 2012.
The differences were mainly driven by differences in mortality among children under one.
Lead author Dr Ania Zylbersztejn, of UCL Great Ormond Street Institute of Child Health, said: "While child deaths are still rare, the UK has one of the highest child mortality rates in western Europe.
"Babies born prematurely or with low birth weight have an increased risk of early death, and those who survive are more likely to have chronic ill health or disability."
The higher frequency of adverse birth characteristics such as low birth weight, pre-term birth or congenital anomalies in England were the main reasons for the excess risk of death compared to Sweden, accounting for 77% of the excess risk for newborns, 68% for under-one-year-olds.
Socioeconomic factors explained a further 3% of excess risk in newborns, and 11% in under-one-year-olds.
Combined, they said these factors fully explained the difference in survival for under-fives in England and Sweden.
Good maternal health - including maintaining a healthy weight, avoiding chronic illnesses such as diabetes, high blood pressure, psychological stress and infections - and health behaviours - such as a healthy diet, and avoiding smoking, drugs and alcohol - are associated with healthy foetal development during pregnancy.
However, many adverse maternal characteristics are more common in England than in Sweden.
The UK has one of the most unequal distributions of wealth of all western countries.
From 2003 to 2005, the most deprived 20% of the UK's population had a seven-fold lower income than the least deprived 20%, while the gap in Sweden was only four times.
This suggests many more people in England are socioeconomically disadvantaged, which is associated with pre-term birth, low birth weight, birth anomalies and poor maternal health, reflecting circumstances and behaviours linked to poverty and stress.
Professor Anders Hjern, of the Karolinska Institute, Sweden, said: "This study shows that the main explanations for the differences in child mortality rates between England and Sweden are systemic, and beyond the reach of healthcare services alone.
"The key factors here are likely to include Sweden's broader welfare programmes that have provided families with an economic safety net for over 50 years, the free and accessible educational system, including early child care, and public health policies for many lifestyle issues such as obesity, smoking and alcohol use."