BRISBANE, July 12 - Department of Education and Training data shows 1028 children aged four and five were suspended in 2016, almost double the 572 in 2013.
They were banned for behaviours including physical and verbal misconduct, and persistent disruption.
Queensland Teachers' Union president Kevin Bates said the increase in suspension rate was partly because this level of schooling was only introduced in 2008.
"We now have 99 per cent attendance and as a consequence, these sorts of things tend to come to the fore," he said on Wednesday.
But Bates was concerned about what was causing children as young as four and five to act out.
"Some of these behaviours result from students who are ill-prepared for school," he said.
"There's a real issue with how well children are socialised before they come to school and how well they've been offered opportunities to begin their learning."
Bates said daycare and home environments had "an impact".
However, Bates and the education department told AAP the number of suspensions was relatively small - equating to about 1.1 per cent of prep students.
In contracts, more than 73,000 students from prep to year 12 were excluded from school for one or more days during 2016.
"The great majority of state school students from prep to year 12 behave appropriately every day, are actively engaged in learning and have positive relationships with their fellow students and teachers," a department spokeswoman said.
"We support principals in taking strong disciplinary action where a student's behaviour is unacceptable."