US President Joe Biden has described the start of the vaccination campaign for children aged six months to five years as a "historic milestone".
The availability of the corona vaccination for the little ones is a "significant step forward," said Biden in the White House on Tuesday.
"Nearly every American can now have access to life-saving vaccines," he said.
Biden appealed to all parents to have their children vaccinated.
The vaccines were approved after "extensive scientific review" and are "safe and effective," stressed the President.
If parents have any questions, they should discuss them with their doctor.
Biden also called for the vaccinations not to be used politically.
"This is no time for politics.
It's about parents being able to do whatever they can to protect their children," Biden said.
Immediately before, Biden had visited a vaccination center for children in the capital Washington.
After an advisory committee to the US Food and Drug Administration (FDA), the health authority CDC also spoke out in favor of the use of coronavirus vaccines in children between the ages of six months and five years.
Both the vaccine from the manufacturers Biontech and Pfizer and the preparation from Moderna could be used for around 18 million small children, it said.
Previously, Biontech/Pfizer's vaccine was approved in the US for children ages five to 11, and Moderna's vaccine for adults.
Last week, however, the FDA advisory committee advocated approving the Moderna vaccine for children and adolescents between the ages of 6 and 17.
There is currently no corona vaccine approved for very young children in the EU.