Jason Scott Francis was employed as a casual worker at a southern Canberra childcare centre where he committed the "egregious breach of trust" in December last year that left the boy suffering psychological scars weeks after his physical injuries healed.

Francis, 43, pleaded guilty to assault occasioning bodily harm and fronted the ACT Magistrates Court on Thursday when it heard he initially yelled aggressively at the child.

"You were playing with the toys, you should help pick them up," he said.

After being thrown, the boy sustained grazes to various parts of his face.

The incident was witnessed by numerous other people, including other staff members.

In court, prosecutor Madison Fieldus read out the victim impact statement by the boy's mother, who said his outgoing and friendly personality changed after the incident.

"[He] was shy, sensitive and extremely cautious when it came to simply climbing a ladder at the park to go down the slide," the statement reads.

"We rarely saw [him] smile."

The mother also wrote that her son, described as a daredevil with no fear, had been acting out the incident, including pushing his sister off the lounge.

"He didn't want company and just wanted to be alone ... It's like we had a different child," the statement reads.

The court heard the boy went back to the centre but began to experience vomiting on a number of occasions.

"It broke my heart. I had been sending my little boy back to the place where this traumatic event occurred," the mother's statement reads.

"We know this incident would've affected you, too, Jason," she said.

"While we don't condone or agree with what you did, we also forgive you. We are all only human and we all make mistakes."

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Magistrate Beth Campbell described the offending as "an extraordinary loss of control" and an "egregious breach of trust".

"Clearly this was a very unpleasant incident," Ms Campbell said.

"While the physical injuries were minor, the emotional and psychological effect on [the victim] was much more significant.

"The outburst of anger was unacceptable and it was inappropriate.

"As a professional who's meant to have the children and their best interests at heart at all times, to give into that momentary impulse or lack of self control is unforgivable. More was expected of you."

Ms Campbell noted that Francis otherwise had a good character as he had been working in the industry for 10 years without problems.

She sentenced him to a 12-month good behaviour order and 148 hours of community service.

The court heard that Francis had spent about 10 weeks in pre-sentence custody regarding other offending.

Following sentencing, Francis apologised and said he had time to reflect.

"I fully understand that as an educator, the incident should not have happened," he said.

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