Moderna’s two-dose vaccine is up for the Food and Drug Administration’s authorization in children 6 months to 5 years, while Pfizer’s three-dose shot is under review for children 6 months to 4 years.

FDA staff have reviewed data from the companies’ clinical trials, finding the vaccines were generally safe and effective.

The Vaccines and Related Biological Products Advisory Committee includes physicians, infectious-disease scientists and other health experts. The panel meets regularly to consider vaccines and medicines under FDA review.

After a daylong meeting, the committee is scheduled to vote on whether the FDA should authorize the Pfizer-BioNTech and Moderna shots for young children.

The FDA doesn’t have to follow the panel’s recommendation but usually does.

Should the panel sign off, an FDA authorization is expected to come within days.

The FDA, which regulates medical products, must authorize the vaccines before they can be used outside trials. After the FDA’s action, the Centers for Disease Control and Prevention, which offers guidance to doctors, pharmacies and vaccination sites, would set the policy for the youngsters to get the shots.

Many states and vaccination sites wait for the CDC’s signoff before rolling out shots. Vaccinations could begin as early as June 21, according to the Biden administration.

Children are generally at lower risk of developing severe Covid-19, though hospitalizations increased during the Omicron wave last winter. Health authorities have encouraged vaccinations of children eligible to get the shots to protect not only the children, but also adults.

Peter Marks,

who heads the FDA’s vaccines division, opened up the meeting saying the Omicron surge during the winter resulted in hospitalized children at a rate worse than even a terrible influenza season, and it was important that people “don’t become numb” to pediatric Covid-19 deaths, even if they occur less frequently than in older people.

“Each child lost essentially fractures a family,” he said.

While some parents of children under 5 years are eagerly waiting for shots for their young children, surveys suggest most parents are less enthusiastic.

About 18% of parents surveyed said they wanted to get their child vaccinated right away, while 38% say they plan to wait and see, according to a Kaiser Family Foundation poll conducted in April.

About 27% of parents don’t plan to vaccinate their child at all, and 11% will do so only if they are required, according to the survey.

Pfizer’s request for authorization is based on a 4,526-child study testing three doses of either a vaccine or placebo, with all third doses coming between February and April, when the Omicron variant was prevalent in the U.S.

The study found the vaccine was about 80% effective in preventing symptomatic Covid-19 among the children.

The FDA said in its staff review, however, that the small number of children who became sick during the trial made it too soon to make “definitive conclusions” on the vaccine’s effectiveness.

For the youngest children, side effects included irritability and drowsiness. Side effects in children 2 to 4 years old included pain at the injection site and fatigue, according to the FDA.

The FDA’s review of Moderna’s vaccine was based on studies testing two doses of either the shot or a placebo in more than 6,300 young children.

Agency staff said Moderna’s two-dose vaccine was 37% effective for 2- to 5-year-olds and 51% effective for children 6 to 23 months, in a study conducted when the Omicron variant was predominant.

The FDA said children 6 months to 11 years old had lower rates of side effects than adolescents and young adults, with the exception of fever, which was reported more frequently in the younger age groups.

While the studies of the Pfizer-BioNTech and Moderna vaccines didn’t identify any cases of heart-inflammation conditions including myocarditis, the FDA panel is expected to discuss the issue.

The FDA has identified an elevated risk of the conditions in certain people, particularly males 12 to 17 years old.

The first two Pfizer doses are given three weeks apart, followed by a third dose at least eight weeks later. The two Moderna doses are given four weeks apart.

Write to Jared S. Hopkins at jared.hopkins@wsj.com