In 2016, researchers surveyed more than 20,000 youth ages nine to 19, includingabout 5,200 children and teens who said they had vaped at least once.
Almost one in three young e-cigarette users said they had tried cannabis with e-cigarettes at least once, survey results showed.
According to the study, 12.4% of high school students and 4.5% of middle school students, said they had vaped cannabis.
Vaping is generally considered less unsafe than smoking, because burning tobacco or marijuana generates chemicals that are harmful to lungs. But there is little research on e-cigarettes' long-term effects, including whether they help smokers quit.
US health regulators recently gave the five largest e-cigarette makers 60 days to produce plans to stop underage use of their products.
The report - which was published on Monday in the Journal of the American Medical Association (Jama) Paediatrics edition - suggests that more and more children are using the electronic device to inhale marijuana vapour. That included one-third of those who ever used e-cigarettes.
"Smoke from cannabis contains numerous same toxins, irritants, and carcinogens as tobacco smoke", said lead study author Katrina Trivers of the U.S. Centers for Disease Control and Prevention in Atlanta.
It's unclear whether marijuana vaping is increasing among teens or holding steady. The devices have grown into a multi-billion industry, but they are relatively new. "There are a variety of ways that cannabis or marijuana could be used in an e-cigarette, such as putting hash oils, waxes, and other THC liquids directly in the e-liquid section of an e-cigarette".
It was the first time a question about marijuana vaping was asked on this particular survey, which uses a nationally representative sample of students in public and private schools.