How to find COVID vaccines for children under age 5

COVID-19 vaccines began to be rolled out for children between six months and 4 years old across the United States this week.

This means roughly 20 million babies, toddlers and preschoolers under age 5 are now eligible for shots after they were authorized by the U.S. Food and Drug Administration last week.

As of Wednesday, 2.7 million doses of Pfizer-BioNTech's and Moderna's vaccines have been delivered nationwide, the U.S. Department of Health and Human Services told ABC News.

Parents looking to schedule appointments can visit vaccines.gov, a website jointly run by the HHS, the Centers for Disease Control and Prevention and VaccineFinder from Boston Children's Hospital.

Vaccines.gov launched Tuesday, a few days earlier than planned. There are currently 1,591 locations on the website that include a mix of children's hospitals, doctor's offices, community sites, clinics and pop-ups offering the shots.

To use the tool, people can click on the button on the homepage that reads, "Find COVID-19 Vaccines."

On the next page, users enter their ZIP code and click on the type of vaccine, depending on the age group they would like to receive.

It's important to select the correct age group because Pfizer's three-dose vaccine for kids is three micrograms each, one-tenth the dose offered to adults, while Moderna's two-dose vaccine is 25 micrograms each, one-quarter of its adult-sized dose.

Dr. John Brownstein, an epidemiologist at Boston Children's Hospital and an ABC News contributor, said the number of locations is expected to increase to more than 10,000 in the coming weeks are more locations get their shipments delivered

"Of course, we understand there's a lot of anxiety and parents have been waiting a long time to get these vaccines," Brownstein said. "At some point, the supply will outstrip the demand. Any parent will have access in the coming days. It will take time to get vaccines, but there will be enough to supply."

The Biden administration has said it eventually expects that 85% of kids under age 5 will live within five miles of a potential vaccination site.

"HHS has received orders for approximately 4.2 million doses to date," the agency told ABC News. "We made 10 million doses of vaccine available for ordering initially, with millions more available soon, so supply should not be a barrier to someone getting their young child vaccinated."

For those who may not have access to the internet or are not internet literate, they can call 1-800-232-0233, which offers help to schedule appointments in English, Spanish and other languages.

Brownstein also recommends that people contact their family physicians or pediatricians to either schedule an appointment or ask where to find appointments.

"It absolutely makes sense [to contact them]," he said. "That's where you have a formal relationship."

It could prove challenging to get this youngest age group vaccinated if it's not convenient to do so.

According to the CDC, only about 30% of American children between ages 5 and 11 have been vaccinated compared to 75% of kids above age 12.

Adding to the challenge is that many young children will not be able to receive their vaccines at pharmacies, because many states do not allow pharmacists or trained pharmacy staff members to vaccinate children under 3 years old.

ABC News' Cheyenne Haslett contributed to this report.