Assaults by children aged five or under led to 2,600 suspensions from schools in England in 2007-8, figures show.
The figures, highlighted by the Tories, show an increase of 150 suspensions on the previous year and reveal that of the assaults, 1,650 were on adults.
The Conservatives say there is an "increasing problem" with the behaviour of very young children.
The government says exclusions across the school population are falling and its behaviour policy is working.
As a whole, permanent exclusions - or expulsions - have fallen in all types of state schools in recent years, but there has been an increase in suspensions or temporary exclusions.
Teachers' powers
England's schools inspectorate Ofsted, in its annual report this autumn, said behaviour in 95% of primary schools was good or outstanding and that it was satisfactory in 5%.
The new figures show the total number of suspensions of the youngest pupils for assault but not the actual number of pupils involved as the same child might have been suspended several times.
The data was given to the Conservatives in response to a parliamentary question.
The vast majority of infant and primary schools do not exclude any children Iain Wright, Schools Minister |
Shadow children's secretary Michael Gove said: "Children cannot learn if there are other pupils in the class that are acting violently.
"There is a real and increasing problem with the behaviour of the youngest children in primary schools and it makes life impossible for their teachers."
He said the Conservatives wanted to make teachers' lives easier by giving them more powers to keep order, so that possible problems could be "nipped in the bud before they spiral out of control".
A study earlier this year by Ofsted said that exclusion of children aged under seven was still "very rare".
The government says exclusions should be used as "a last resort" - although it backs head teachers' rights to exclude children even for a first or one-off offence.
Schools Minister Iain Wright said: "The vast majority of infant and primary schools do not exclude any children and a recent report by Ofsted, on exclusions of young children, found that almost all children in the schools they visited knew how to behave properly.
"Ofsted are clear that behaviour standards have significantly improved over the last decade, but we know there is more to do to ensure all children learn in an orderly school where discipline is tough and bad behaviour that disrupts the learning of others is not tolerated."
'More aggressive'
He said the government had given teachers and head teachers tough new powers to discipline pupils and would be legislating in the coming weeks for home-school agreements to make sure parents took their responsibilities seriously too.
The Association of Teachers and Lecturers (ATL) recently surveyed its members in primary schools on behaviour in the classroom.
It said that three-quarters of the 1,078 members who responded to the survey said they thought children in primary schools were becoming more aggressive at a younger age.
Just under 61% said they thought behaviour in the classroom had got worse in the past 10 years.