Wem has seen a "significant increase" in the number of coronavirus cases, Shropshire Council has told St Peter's Primary School in Wem.
Parents have been reassured the children affected have not been in school.
But the head at St Peter's is asking parents to review their decision to send children to school in light of the situation.
Allyson Brown, in a letter to parents, said there had been a rapid increase in infection rates amongst children within Wem in the last few days.
She said: "Over the last few days we have been notified by the local authority of a significant increase in the number of children testing positive for Covid within Wem. Fortunately, these children have not been in school and therefore the school does not need to take action at this time.
"However, I wanted to highlight that during the first lockdown we had an average of 20 key worker children attending school each day. In this lockdown, when the pandemic is far worse than it was in March, we now have 136 key worker children on our registers.
"I am now asking you to review your decision to send your child to school in light of the more stringent government guidance and the rapid increase in infection rates amongst children within Wem in the last few days."
She said that the more children in school the more likely it is that Covid was introduced into the setting.
"If bubbles have to close this will not only affect all children and their families within that bubble but will also have a significant impact on those key worker parents who are currently working in frontline services within the NHS and healthcare as they will be unable to attend work at a time when their services are in crisis. We are also placing school staff at an increased risk of infection," she said.
"We must take this situation seriously and do everything we can to stay at home, protect the NHS and save lives."