The drug company Moderna has begun a study that will test its Covid vaccine in children under 12, including babies as young as six months, the company said on Tuesday.

The study is expected to enroll 6,750 healthy children in the United States and Canada.

“There’s a huge demand to find out about vaccinating kids and what it does,” said Dr. David Wohl, the medical director of the vaccine clinic at the University of North Carolina, who is not involved the study.

In a separate study, Moderna is testing its vaccine in 3,000 children ages 12 to 17.

Many parents want protection for their children, and vaccinating children should help to produce the herd immunity considered crucial to stopping the pandemic. The American Academy of Pediatrics has called for expansion of vaccine trials to include children.

Each child in Moderna’s study will receive two shots, 28 days apart. The study will have two parts. In the first, children aged 2 years to less than 12 may receive two doses of 50 or 100 micrograms each. Those under 2 years may receive two shots of 25, 50 or 100 micrograms.