It's alleged the woman took her two sons to the river about 5.30pm on Thursday.
Police are continuing to search for a boy feared drowned in the Murray River, as his mother - who allegedly held her two sons under the water at Moama on the Victoria-New South Wales border on Thursday - is due to face court accused of the attempted murder of his brother.
"The dog is four years old and it's never attacked one person, has grown up with kids, and it's always been around kinds playing", she said.
Authorities launched a major search operation involving police from Deniliquin Local Area Command, SES, and Maritime Rescue, and the Victorian police airwing.
The 27-year-old faces one charge of attempting to murder her son but acting prosecutor Miles Rogers said more charges were expected.
Police told a Deniliquin Local Court hearing that the woman tried to drown the nine-year-old in the Murray River, but he managed to get away, NewsCorp Australia reports.
She's been charged with attempted murder.
The mother, who can not be named, is expected to appear in court via videolink on Monday.
The nine-year-old son is in a serious but stable condition in the Royal Childrens' hospital in Melbourne after also suffering serious dog bites on Thursday evening.
The father of the boys has spoken of his devastation and said he was numb after learning about what had happened.
That same night, a nine-year-old boy, his older brother, was being rushed from the scene to hospital with serious dog-bite injuries.
"We had made considerable representations to Family and Children Services and the Department of Correctional Services about the imminent risk posed to the little boys with their mother's release from prison", the statement read.
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"So far the search has involved searching the riverbank where [the boy] was last seen as well as using Victoria Police divers to search the river".
"The mother in this instance has been a really troubled individual, she's been a long term ice addict". The Bendigo Magistrate's Court also heard she allegedly told witnesses the night before that she "had to drown my babies".
The boys reportedly had been living with their grandmother for the past year, and even though the grandmother had taken out an apprehended violence order against her daughter last year, the woman had moved into the house upon her release from prison.
A dog that belonged to a nearby property owner then bit the boy as he fled up the riverbank.
Supt Condon said neighbours found the boy and told police they had taken him to the hospital.
He said the grandmother had complained to government agencies numerous times about the woman's behaviour and tried to get her removed from her home.
Shortly after, Brooks said the woman took the grandmother's vehicle, snatched the two young boys and left with a couple of her buddies.
"I think they (the agencies) have some culpability in this case". And the child (in hospital) has lost his mother and probably his brother, it will change his life forever.
Deniliquin Superintendent Paul Condon said the tragedy will be felt around the country.
Police spoke to the 9-year-old briefly last night.
The incident happened at Moama, near the Murray River.