The agency claimed that if reduced speed limits were put into practice, around 13,000 children could be saved from death and injury each year.
Its urgent plea for action comes after it unveiled evidence on the best ways to improve the safety of vulnerable groups at a conference in London.
The evidence, which is based on a review of research from around the world, also highlights the fact that children from poorer social classes are at a higher risk of accidental death than richer groups.
It shows that the death rate for pedestrian accidents is five times higher for children in the lowest social class compared with those from the highest social class.
This latest demand for a 20mph limit follows similar calls from the Accidental Injury Task Force and the Institute for Public Policy Research.
The agency says it will work with local authorities to support the introduction of 20mph zones in disadvantaged areas in an attempt to reduce the disproportionate toll of road injuries suffered by these communities.
Professor Mike Kelly, the agency's director of research and information, said: "As well as putting 20mph speed restrictions into place, there needs to be a firm resolve to enforce these measures.
"Roads have been car-focused for too long. It's time for a balance that improves safety for the whole community."
Prevention and Reduction of Accidental Injury in Children and Older People is available free from the Health Development Agency (tel) 0870 121 4194.