A Hartlepool nursery worker 'popped' a little boy's elbow as she pulled him apart from another child.
Terri Chapman told a colleague: "I'm going to get the sack' when she realised she had caused an injury.
A nurse was able to reset the child's elbow with no lasting ill-effects, a court heard.
CCTV footage from the nursery in Hartlepool showed the boy, who was in the aged three to five group, crawling under a table after Chapman lifted him off his feet by one arm.
"Chapman is described as sometimes being moody and showing a negative attitude to the children," said Emma Atkinson, prosecuting, at Teesside Crown Court.
"On the morning of this offence the boy can be seen on the CCTV playing with another boy.
"Chapman is seen to separate them by pulling the boy by his wrist, lifting him off his feet.
"She then puts him on the floor, and he crawls under a table."
A few minutes later Chapman pulls the boy from under the table by his feet.
"It's then apparent to her his left arm is injured," said Ms Atkinson.
"She took the boy to a kitchen area before approaching colleagues to tell them what she'd done, remarking that she would be sacked for it.
"The elbow is described as being 'popped back' by a nurse.
"Chapman was suspended, and has since left the nursery,"
The court heard the boy's grandmother said he refused to return to the nursery for two days, but has since been happy to return.
Chapman, now 22, of Navenby Grove, Hartlepool, admitted assault occasioning actual bodily harm on June 28 last year. She was 20 at the time of the offence.
She was of previous good character.
Stephen Constantine, defending, said in mitigation: "There was no intent to cause any injury, and Ms Chapman is devastated to think she caused an injury to a child.
"Walk down any street and you may see a child being held in the air by an arm with no ill-effects.
"Ms Chapman was clumsy when she separated the boy from the other child, but no more than that.
"As soon as she realised what she'd done, she owned up to colleagues and sought help for the child.
"She accepts the career she wanted to pursue in childcare is at an end, and she now has a job that doesn't involve children."
Judge Howard Crowson sentenced Chapman to a community order of 12 months, 80 hours of unpaid work, and ordered her to pay £100 costs.
The judge told her: "You were clumsy in the way you separated the two children, but there was no intent to cause harm.
"The boy must have been in some distress, but it was not vocal distress.
"He hid under the table, as little boys sometimes like to do.
"There were other staff members present, and they would have been bound to attend to him if there was any indication he was injured.
"When you discovered the injury, you made no effort to conceal what you did, even though you knew it would mean the end of your childcare career.
"The public would expect some punishment, but it is unlikely you will offend in this or any other way again."