While overall child mortality fell by 50% in the past 20 years in UCL Institute of Child Health report, young maternal age was found to be a risk factor for death in early childhood.
Support should be extended to mothers of all ages, not just first-time teenage mums, the report's authors concluded.
Ruth Gilbert, lead researcher and professor of clinical epidemiology at UCL Institute of Child Health, said the findings showed the need for universal policies to address healthcare disparities.
"Young maternal age at birth is becoming a marker of social disadvantage as women who have been through higher education and those with career prospects are more likely to postpone pregnancy until their 30s," she said.
'Unexplained causes' of child deaths
The research found that in England, Scotland and Wales, the difference in mortality between children of mothers under 30 and those born to mothers aged 30 to 34 accounted for 11% of all deaths up to nine years old.
This is equivalent to an average of 397 deaths in the UK each year. Deaths in children born to mothers under 20 accounted for just 3.8% of all child deaths up to nine years old.
The study compared children with similar birthweight in each age category and reported that the biggest difference in deaths was in infants aged from one month to one year.
Among this age group, 22% of deaths in the UK were due to "unexplained causes", the report said, "which are strongly associated with maternal alcohol use, smoking and deprivation".
The report added that the current policy, which focuses support on teenage first-time mothers, was not wide-ranging enough because mothers aged under 30 account for 52% of all births in the UK.
Young, disadvantaged mothers
Jill Rutter, head of policy and research at the Family and Childcare Trust, said the findings showed government needed to do more for young, disadvantaged mothers.
"Disadvantage and maternal age are factors often associated with child deaths. The government has recognised the vulnerability of the children of teenage mothers and given these families extra help with parenting.
"In England the Family Nurse Partnership is an intensive, structured, home-visiting programme, which is offered to first-time parents under the age of 20.
"A specially trained nurse visits regularly from early pregnancy until the child is two years old. This project has excellent results, but is not available to older mothers.
"We would like the Family Nurse Partnership to be extended to take older mothers who need help."