Childcare organisations are demanding to see evidence that it is safe for them to remain open while schools and colleges have closed to most pupils.
Staff have close contact with children and babies daily, when they change nappies and receive them by the hand from parents, for example.
Ministers have insisted early years settings are safe as young children have very low rates of the virus.
Nurseries argue the evidence cited is based on data about old variant Covid.
England's three main nursery organisations, the Early Years Alliance, the National Day Nurseries Association and childminders' group, Pacey, have joined together to mount a #ProtectEarlyYears campaign.
They want the government to provide clear scientific evidence on the risks to early years staff of staying open, particularly in light of the increased transmissibility of the new variant of Covid-19.
Sue Cardy, owner and manager of Ready Teddy Go Pre School, in Shoeburyness, Essex said: "There isn't anyone who has asked: 'Is it 100% safe for us to remain fully open? No one can see the virus and staff may be asymptomatic, and so we all run an element of risk of catching or spreading it."
She added: "Staff have families and are not all young... 50% of my staff are over 50 and some have underlying medical conditions."
Vicky, the manager of a church pre-school in Cheshire West and Chester said she could potentially have 30 children plus 10 staff in a church hall, with no PPE recommended, and limited social distancing.
"As an early years provider, I am increasingly worried about the safety of both staff and children, yet if we chose to partially close, we could be financially penalised."
And Georgie Morrell from Brighton and Hove said: "Since re-opening, I have had four households tell me. they are Covid positive.
"This is clearly very close to home and yet we have been given no choice or support but to remain open and carry on."
Neil Leitch, chief executive of the Early Years Alliance, said: "It is simply not acceptable that, at the height of a global pandemic, early years providers are being asked to work with no support, no protection and no clear evidence that is safe for them to do so.
"We know how vital access to early education and care is to many families, but it cannot be right to ask the early years workforce to put themselves at risk. That is why it is vital that the government takes the urgent steps needed to safeguard those working in the sector, particularly mass testing and priority access to vaccinations.
Nursery providers are calling for staff to be tested, priority for vaccination and for state funding lost due to lower numbers during the pandemic, to be replaced by government.
Purnima Tanuku, chief Executive of National Day Nurseries Association, said nurseries were determined to support families during the current lockdown.
But, she added: "Time and again, whether it's on PPE, cleaning costs, testing or staffing, early years providers have been overlooked by the Department for Education.
"Now, they are the only part of the education sector fully open to all children and must be given priority."
On Wednesday, vaccines minister Nadim Zahawi said there was very little risk to younger children.
"The nursery sector has taken tremendous care in making sure the premises are also Covid safe. It is the right thing to do."
The Department for Education is yet to comment on the #ProtectEarlyYears demands.