Local authority chiefs fear they could be overwhelmed by the work involved in implementing the Children Act 2004.
One director of education said 2008 was set to be an "annus horribilis"
because of the new legislation, and a range of other changes due at the same time.
The Act seeks to improve services by encouraging a more joined-up approach between the agencies that work with children.
Under the Act local authorities must have a children and young people's plan (CYPP) in place by April 2008. This three-year strategic vision includes key targets and priorities and sets out how authorities, schools and other partners such as the health and voluntary sectors will work together. Every local authority, NHS trust and health board will be required to have a lead director and lead elected member responsible for overseeing joint working arrangements for children's services.
Chris Llewelyn, director of lifelong learning at the Welsh Local Government Association, admitted there was "considerable anxiety" within local authorities about their capacity to deliver the changes and meet the 2008 deadline.
Speaking at a seminar on the implementation of the Act at last week's WLGA conference in Llandudno, he added: "There's concern about the dynamic policy environment in which we're operating, and the difficulty of implementing changes in the context of education.
"We're already having to deal with a range of changes such as the foundation phase (for three to seven-year-olds) and learning pathways (for 14-19). There is a capacity issue."
Richard Parry Jones, Anglesey's director of education and leisure, said:
"We're worried about the quantity of work that will have to be accomplished in the time available. If this is to be implemented in April 2008, we'll have to have it ready by late 2007, because it will have to go to the Assembly government for approval. I'm concerned this timetable is extremely tight."
Mr Parry Jones urged David Middleton, the Assembly government's head of the children's framework, for as much information as possible to avoid any "late surprises".
He added: "2008 is rapidly becoming an annus horribilis. There are a number of other initiatives we've to deliver and this is only one of them."
Mr Middleton said the government was "not wedded" to the April deadline and stressed that a consultation period next year would allow these concerns to be considered.
"We're not intending to force people to do something that isn't going to be fit for purpose," said Mr Middleton.
He added: "No single agency can deliver the range of services children need. There is a need to bring greater coherence and focus into the planning system."
Sue Essex, minister for finance and public services, told the WLGA conference that too many young people are excluded if they "don't fit into the right holes".
The central ethos of the Children Act is to cover all bases by listening to young people and providing a more unified service.
Schools are central to this aim and are expected to be involved in children and young people's partnerships and plans. The government thinks this can be achieved through existing structures such as clusters of schools.
An Assembly government spokesperson said: "The involvement of school representation in partnerships will enable them to be involved directly in the development of integrated services."