NSW Police and Government agencies are undertaking a full-scale probe following Thursday night's incident at the Murray River.
A 5 year old boy's body was found by search crews Saturday morning, 2 days after he was reported missing from a Moama address.
His 9 year old brother remains in a Melbourne hospital in a stable condition, treated for serious dog bites inflicted during the incident.
The boys' 27 year old mother is still in custody and expected to be charged on Monday with murder.
It's expected she will appear via video link at Deniliquin Court.
She's already been charged with attempted murder.