Graham Archer, director of children's social care, improvement and learning at the DfE, told delegates at the Association of Directors of Children's Services (ADCS) annual conference in Manchester that the "difficult fiscal position" meant it was unlikely "a lot more money" would be allocated to council children's services at the 2019 spending review.
Archer was responding to warnings from ADCS president Stuart Gallimore that there is "no fat left to trim" from children's services budgets as a result of local government funding cuts and significant rises in the number of looked-after children, child protection plans and Section 47 inquiries in recent years.
Children's minister Nadhim Zahawi, speaking after Gallimore acknowledged that funding is a "real challenge", adding that he is "listening" and wants to to work with the sector "to understand the evidence for additional investment".
The Local Government Association (LGA) has previously warned there will be a £2bn funding gap by 2020 in the amount councils spend on children's services and how much they receive from government.
Archer said the sector and the department will need to work together to analyse the factors influencing demand and spend in children's social care and how these related to performance and quality to improve understanding of whether more money is needed, better commissioning of services or greater roll out of good practice.
"We could do all of that and do it brilliantly and it could prove what you say [about needing more funding] but I'm not that confident it would be a blueprint for a lot more money coming into the system," he said.
"This will be a very difficult spending review and these conversations [about funding] will be going on elsewhere in the public sector - the NHS, education, adult social care.
"If we do get the evidence right and have a common view on what the evidence tells us there's a better chance of a [positive] decision being taken for children's social care."
Archer said he welcomed recent research from Newton Europe, commissioned by the LGA and published last week, that found half of the variation in spending between children's services is down to deprivation and other societal factors outside their control.
Local government and children's services leaders have said the research supports their calls for more money but Archer said more analysis is needed before any conclusions can be drawn from it.
"We need to test some of these hypotheses and we want to do that quickly," he said. "We have to be really sharp about the evidence that we bring to the table. You shouldn't assume your certainties about the position you see in your authority are shared."