A new study finds a significant and steady increase in the number of children in the United States who are admitted to pediatric intensive care units (PICUs) after swallowing opioids.

The increase occurred across all age groups, researchers report in the journal Pediatrics. The opioid-related PICU admission rate increased 39 percent from 2004 to 2015, HealthDay reports. The majority of these patients were ages 12 to 17, but a third of patients were younger than 6.

“What concerns us is the rate that PICU admissions are increasing over time, which is in contrast to adult data that suggest we have reached a plateau in hospitalization for opioid overdose,” lead researcher Dr. Jason Kane of the University of Chicago Comer Children’s Hospital said in a news release. “As more opioids are being prescribed in the community, children are becoming ‘second victims’ of the opioid epidemic.”