Concerns for the wellbeing of babies born in lockdown are being raised, as parents struggle to access regular support services.
England's children's commissioner is highlighting pressures facing mothers caring for babies without the usual family and state support networks.
Playgroups are closed and health visitor "visits" are being carried out remotely in most cases.
The NHS said adaptations had been made to keep new mothers and babies safe.
Most health visitors checks are being carried out remotely at the moment. Getty Images
The briefing paper from Anne Longfield's office says an estimated 76,000 babies will have been born in England under lockdown so far.
But births are not being registered, because of temporary rules tied to the virus pandemic, so even basic information about new babies is not being gathered.
At the same time, support services provided by health visitors and GPs are not readily accessible, with many taking place via phone and video calls or not at all.
She highlights how up to 50% of health visitors in some areas of England were redeployed to other parts of the NHS as it grappled to fight the pandemic.
And there are concerns many babies may have missed their developmental health checks, due in the first few weeks of life to pick up urgent developmental needs.
Institute of Health Visiting executive director Dr Cheryll Adams said health visitors were very concerned.
"In some areas, the six-week GP baby check hasn't been available or parents haven't wanted to attend it due to a potential risk of infection," she said.
And, although helplines for parents had been set up in most areas, the usual sources of support from family, friends and voluntary services were no longer as available.
Ms Longfield said: "At the best of times, around 10% of new mothers face perinatal [post-birth] mental illness - but the GP is closed, as is the children's centre and playgroups and playgrounds, and the health visitor, where she 'visits', is doing so by video link.
"There are even reports that in some areas families have been stopped from playing outside together by heavy-handed policing of lockdown rules.
"The vast majority of new parents will be coping - the resilience of the family will see them through.
"But there will be a significant minority where the additional challenge of a new child is a strain too far."
Ms Longfield is particularly concerned about children living in poverty or with risks such as domestic violence or mental ill health.
"Health services are usually the places where concerns about babies are identified and referred - and these services are likely to remain under increased pressure for a long period of time," she said.
Proactive steps were needed to ensure different agencies shared information on children they had concerns about, she said.
And she called for ministers and local authorities to prepare for a surge in referrals to social services and post-natal services as lockdown eased.
Public Health England chief nurse Prof Viv Bennett said: "Many community nursing services have been provided virtually and innovatively during the Covid-19 response.
"With the onset of Covid-19, some public health nurses were redeployed in hospitals where their expertise was most needed to care for acutely ill patients.
"It is important that as pressures ease, these nurses are able to quickly get back to help support those families and young people."