Treating depression and other mental disorders in U.S. children cost $8.9 billion in 2006, making mental illness the most expensive condition to treat in childhood, U.S. government researchers reported on Wednesday.

An estimated 4.6 million children were treated for mental disorders in 2006 at an average cost of $1,931 per child, the Agency for Healthcare Research and Quality reported.

But more children were treated for asthma than any other disease or injury, the AHRQ found. It said nearly 13 million children were treated for asthma in 2006 at an average cost of $621 for a total of $8 billion.

Fractures, sprains, burns, and other physical injuries from accidents or violence sent 7 million children to doctors or clinics at a cost of $658 per child or $6.1 billion, the survey found.

The agency gathered data from the Medical Expenditure Panel Survey for the report.