The children’s commissioner for England has backed mandatory tracking of youngsters by local authorities, saying no one knows how many children there are in the country.

The recommendation came in a report initiated by Rachel de Souza, the children’s commissioner, which surveyed all 151 English local authorities and found many did not have figures for the number of children being home-schooled or attending independent schools in their region.

The survey also found that most councils relied on updated census figures from the Office for National Statistics to estimate how many children were in the local authority, although a few also used GP enrolments or other data.

“From the survey we have conducted we have found that [local authorities] do not have an accurate figure of how many children there are in England – let alone the number of children not receiving education,” de Souza said.

“It is crucial that we know where all children are, and that we develop the necessary infrastructure to maintain this understanding.”

De Souza said that “there are hundreds of children that have never interacted with the education system that we know nothing about”, including children who may have gone missing from care or been trafficked into the UK.

The report calls for local authorities to collect and access more regularly updated data on children and their movements, including on immigration from the Home Office.

One option would be a “unique identifier” for each child on databases that “would enable [local authorities] to better track children who move around the system. Having a single unique identifier would better enable services to share information on a child, identify where they need help, and allow services to support them back into school.”

The Local Government Association said: “We were pleased the government recently acted on councils’ concerns by introducing a register of children not in school, to help councils to ensure that children are receiving a suitable education in a safe environment.

“However, the safety net that schools and councils provide to ensure that children do not miss out on their entitlement to education is stretched to capacity, exacerbated by a lack of resources and powers available to councils to fulfil their statutory duties – which worsened as a result of the pandemic.

“We would like the government to work to raise the profile of children missing formal full-time education, and to resource councils adequately to fulfil their responsibilities in ensuring all children receive a suitable education.”

The Department for Education was contacted for comment.

De Souza’s report estimated that 22% of state school pupils, or more than 1.7 million, were “persistently absent” in the 2021 autumn term. That would agree with official data showing hundreds of thousands of children absent from school with confirmed and suspected cases of Covid-19, with more absent ill with Covid symptoms.

A pupil is counted as persistently absent if they miss 10% of classes. A child isolating with Covid for seven or more days in one term would be classed as persistently absent.

The DfE’s latest figures show that school attendance in England is returning to normal, with just 0.7% of pupils and students absent for Covid-related reasons on 3 March, compared with 2.2% in February.

Overall attendance rates in state primary schools was 95% and those in state secondary schools were above 89%.