Schools can decide whether or not to reopen in June, Public Health England's medical director has said.
Ministers' plans to open primary schools to pupils in Reception, Year 1 and Year 6 from June 1 look increasingly in doubt amid a backlash from the sector.
Some 68 councils have refused to follow Boris Johnson's timetable with unions insisting the plans would put teachers, parents and children at risk.
But Professor Yvonne Doyle told MPs on Friday morning that schools can decide on a local basis whether they reopen.
She told the Commons science and technology committee: "The children who are being invited back to school will be young children and Year 6, and this will be on a phased basis.
"But ultimately, it will be for schools to decide whether they are ready for this and whether parents have confidence that they will send the children back."
She added that PHE has a "very clear view" that "it is good" for schools to return as soon as possible and that the science shows "the risk to children... seems to be much lower" than adults.
However, she said "practicalities" over reopening for some schools and ensuring hygiene measures means it will be a "trade-off" for schools to decide.
The Government is due to publish its scientific advice on reopening schools later today.
Independent Sage, the rebel group of scientists led by ex-chief scientific adviser Sir David King, have waded into the row insisting the risk to children would be halved if the reopening date was pushed back two weeks.
It comes after Justice Minister Robert Buckland appeared to signal Number 10 was rowing back from its plan for a phased reopening to begin from June 1.
He said earlier this week that the Government would listen to the concerns of councils and headteachers and that there would be no "uniform" reopening until after the half-term.
Ministers have been at loggerheads with teaching unions, which have said the Government has failed to produce scientific evidence to show reopening schools in 10 days is safe.
Official guidance for school leaders urges pupils to be taught in small "bubbles", with class sizes of no more than 15 and staggered pick-up times and break times.