Some councils are incorrectly using their children and young people's plans as commissioning strategies, a Community Care conference was told last week.
Keith Moultrie, deputy director of the Institute of Public Care, said authorities had told him that their plans were detailed enough to constitute a commissioning strategy.
But he said there was a fundamental difference between the two documents.
"A children and young people's plan covers the whole population of children," he said. "A commissioning strategy is much more specific about the configuration of services that are required, down to the allocation of resources."
Meanwhile, a senior civil servant at the Department for Education and Skills revealed that research to be published soon would show that some councils may be failing to achieve adequate value for money in their children's services.
Anne Jackson, director of the DfES's children, young people and families strategy group, said reports would show wide variations between the costs of certain services across councils.
The research into council services undertaken by accountancy firm PricewaterhouseCoopers, to be published at the end of the summer, will look at the impact of commissioning on the children's services market.