More kids, especially girls, are attempting suicide. It's not clear why.

“When we looked at hospitalizations for suicidal ideation and suicidal encounters over the last decade, essentially 2008 to 2015, we found that the rates doubled among children that were hospitalized for suicidal thoughts or activity,” Dr. Gregory Plemmons of Vanderbilt University told NBC News.

Plemmons and colleagues analyzed a database of visits at 49 children’s hospitals for kids aged 5 to 17.

Although suicide ideation — thinking about suicide — and suicide attempts accounted for just 1 percent of all hospital visits, the numbers have steadily increased,

Half of the encounters involved teens aged 15 to 17; 37 percent were 12 to 14; and almost 13 percent were children aged 5 to 11 years. Girls made up nearly two-thirds of the cases.