The little girl's family say the news has caused them more pain, coming after what they consider to be a too-lenient sentence.

Brendon Toohey was convicted of the sexual assault of the infant in Parramatta District Court on March 7 in a judge-alone trial.

The notice of intention to appeal lodged by Toohey last month means he has six months to lodge the actual appeal. A date will then be set for hearing in the Court of Criminal Appeal.

Toohey had entered a plea of not guilty, with the judge returning a guilty verdict on the day.

Toohey was convicted in 2017 of the manslaughter of the same 11-month-old infant and was jailed for seven-and-a-half-years. 

A non-parole period of four-and-a-half years made him eligible for parole on October 8 last year.

The charge of sexual intercourse with a person under 10, under authority, was heard separately from the manslaughter charge.

For this, Toohey was sentenced to a jail term of four years and six months (three years non-parole) to date from March 9, 2016, which made Toohey eligible for parole on March 8, 2019, the day after he was sentenced.

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The family of the baby girl say hearing about Toohey's intention to appeal has shocked them.

"I still don't know what to say. The whole thing has been unbelievable - the whole lot," the girl's paternal grandmother said.

She said the police and the Director of Public Prosecutions had been great through the whole process, but she said the courts had let the family and the baby girl down.

"Everyone has done their utmost [to get justice], but when it went through the door of the court, it was out of their control," she said.

"The police have done an outstanding job, so has the DPP; they have been absolutely wonderful and we can't thank them enough. But when it went to court that's when everything changed."

She said the family would continue to fight to ensure what happened wasn't forgotten.

Toohey was charged by police in the weeks following the infant's death in 2014.

He maintained the child suffered critical injuries after falling from a trampoline and hitting her head.