California is in the midst of an unprecedented decline in its child population. Falling birth rates, a decrease in migration and the retirement of the 'baby boom' generation are threatening the future prosperity of America's most populous state, a new report has revealed.

The report, by the University of Southern California (USC), shows that in 1970 children made up one third of the state's population. By 2030 that number is expected to have declined to one fifth.

"After decades of burgeoning population and economic growth the state now faces a very different prospect," the report, titled California's Diminishing Resource: Children, said.