By Hannah Goff
BBC News at the NUT conference, Manchester
The NUT says nursery school children must enjoy themselves
Nurseries should be led and managed by qualified teachers who can pick up child development problems, a teaching union is to argue.
The National Union of Teachers' conference will also hear calls for a reduction in the formal assessment of children as young as three.
It will argue that early academic teaching could distort a child's natural way of learning through play.
The NUT's leader said the early years curriculum must not be "too tick box".
General Secretary Steve Sinnott said there were issues about introducing the kind of curriculum seen in the first years of primary school too early.
He warned it would be the worst thing if a new early years curriculum, due to be made compulsory in September, became too tick box.
"The most important thing is that young children really enjoy themselves and are open to ideas."
Teachers will also debate calls for more play and fewer tests in primary schools.
A separate motion argues that play is crucial to the development of children and can give children more confidence to learn.
Mr Sinnott said early years teachers were highly skilled and able to use their professional judgement to spot development problems.
"If the teacher believes a three-year-old doesn't have any language at all, that's what the teacher is going to concentrate on," he said.
A motion, due to be debated at the annual conference on Monday, expresses concern over government plans to ensure Children's Centres are lead by early years professionals by 2010.
It argues that the role of qualified teachers could be undermined by the move.
Despite their high cost, nurseries are mostly staffed by low-paid workers with only basic qualifications.
The motion calls for all government-funded Children's Centres, which offer nursery provision for three to five year olds - often in deprived areas - to be led by qualified teachers.