A class was sent home from a primary school in north Dublin after two Covid-19 cases were confirmed.
An urgent letter was sent to parents and guardians of children at the school informing them of the positive tests.
Health experts said that all those in the class were "close contacts" and must therefore self-isolate.
School officials wrote to parents and explained that the two cases "appear unconnected".
However children in the class will need to be retested next Sunday before their period of self-isolation ends.
The letter reads: "Unfortunately I have to inform you that there have been two cases of Covid in your child's class reported today. At present the cases appear unconnected to each other.
"The HSE have decided that all children and staff in the class are close contacts and are to be tested soon, and retested later in the week.
"I will be sending on your child's contact information today and you should hear from the HSE later today or tomorrow about a test date.
"The children in the class will be retested around 28th March and should restrict their movements until then.
"You will be provided with further information from the HSE on testing."
It comes after at least 20 people have tested positive for Covid-19 after a "frightening" outbreak at an Offaly creche.
The Tullamore creche saw 12 children and eight staff among the confirmed coronavirus cases.
The owner of the creche is said to be "distressed" after the facility "followed all guidance" regarding public health measures.
Both the Federation of Early Childhood Providers and the National Childhood Network described the outbreak as "frightening".
The groups, which represent childcare providers, are requesting a number of changes to help them deal with the challenging conditions.
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They are asking to be placed as a high priority for vaccinations, as essential service providers for essential workers, to get subsidised weekly antigen testing in childcare facilities to protect children and staff and additional PPE grant-aid.
They added: "Many crèches and childcare facilities are now back to around 90% occupancy and workers are worried about the spread of new variants of the Covid-19 virus.
"Childcare workers meet the needs of children and families, so that wider services in society, like healthcare, can be provided and the economy can reopen.
"There is exceptional difficulty in preventing virus transmission when working with young children.
"Vulnerable people work in the childcare sector, including pregnant women and some with underlying health conditions, or they live with a family member that has underlying issues. They need to be protected while providing an essential service."
