Schools in Wrexham will not be reopening for the youngest pupils on February 22 despite Welsh Government confirming schools could do so from that date.
Wrexham Council said it would aim to begin opening schools for those aged three to seven from February 26 "at the very earliest" because of concerns over high levels of coronavirus transmission in the area.
While Covid case numbers are falling across the majority of the country, some places in north Wales have seen their numbers go up in recent days.
Numbers are going down in Wrexham but the council said levels still remain "very high".
Wrexham currently has the highest seven-day rolling case rate of all Welsh local authority areas at 206.7 per 100,000 of the population. Anglesey and Flintshire also have some of the highest rates.
On Thursday, 410 new cases were confirmed across the whole of Wales. Another 27 Covid-deaths were also reported.
Councillor Phil Wynn, Wrexham Council’s Lead Member for Education, said: "Coronavirus levels have been much worse in Wrexham compared to many other parts of Wales in recent weeks, so this is a cautious approach we’re taking.
"We’ll monitor the local situation continually, and will work with schools to review and finalise arrangements after half-term.
"Foundation phase learners will not return until February 26 at the very earliest, and headteachers will keep parents fully informed.
"It’s all about helping to keep people safe, and the wellbeing of our pupils, staff, parents, carers and wider communities is our priority.”
Schools have been closed for face-to-face learning for most pupils since December, when Wales' entered its third national lockdown.
However, last week the Education Minister said: "there is sufficient headroom for us to bring back some of our learners in a phased, flexible and progressive way.
"After half term, from 22nd February, our Foundation Phase learners will start to return to school during that week.
"The youngest learners have been prioritised because they find it difficult to learn remotely, and transmission risks are lower".
Children of critical workers and vulnerable learners, as well as those taking exams or assessments and learners in special schools, will continue to be able to attend as they have done throughout the pandemic.
Following the Education Minister's announcement, the leader of Anglesey Council also said that the authority will “do what is best for schools” as coronavirus cases remain high there.
Cllr Llinos Medi said: “The safety of school pupils and staff is our main priority. We are working with schools and planning for a proposed return to school of Foundation Phase children from Monday, February 22nd.
“If we are not comfortable that the rate of coronavirus cases on Anglesey is safe enough to allow the return of children and staff, we won't be opening our school buildings."