Shares of the Cambridge, Mass. biotech were rising 2.5% to $147.27 in premarket trading.
The two-part Phase 2/3 study, dubbed the KidCOVE study, includes healthy children in the U.S. and Canada. It is intended to evaluate the safety, tolerability, reactions and effectiveness of two doses of Moderna's vaccine, mRNA-1273, given 28 days apart.
Moderna said it plans to enroll about 6,750 pediatric participants. Children who receive the vaccine will be followed for 12 months.
Moderna's COVID-19 vaccine received emergency use authorization from the Food and Drug Administration on Dec. 18, 2020, and the company started supplying the federal government shortly thereafter.
The vaccine is currently authorized by the FDA for adults aged 18 and older. There is no vaccine approved yet for children.
CEO Stephane Bancel said in a statement that it was "humbling to know that 17.8 million adults in the U.S. have received the Moderna COVID-19 vaccine to date."
"We are encouraged by the primary analysis of the Phase 3 COVE study of mRNA-1273 in adults ages 18 and above and this pediatric study will help us assess the potential safety and immunogenicity of our COVID-19 vaccine candidate in this important younger age population," Bancel said.
As of Tuesday, there were 120.3 million COVID-19 cases in the world, according to Johns Hopkins University, with 29.5 million in the U.S. There have 2.7 million deaths worldwide, with 535,661 in the U.S.
White House Chief Medical Adviser Dr. Anthony Fauci in an interview with "Fox News Sunday" that despite vaccinations the nation is now at "absolutely no time to declare victory."
In February, Moderna reported a fourth-quarter loss wider than forecasts but sales that were almost double analysts' expectations as it continued to forge ahead with the rollout of its COVID-19 vaccine.
Separately, Moderna said on Monday that it had dosed the first participant in an early-stage study of a new COVID-19 vaccine candidate that could potentially be stored and shipped in refrigerators instead of freezers, according to Reuters.
The company said its new candidate could make it easier for distribution, especially in developing countries where supply chain issues could hamper vaccination drives.