'Further tests'
Following a search of the property in West Hendon on Tuesday, police revealed human remains had been found.
The two women were then re-arrested along with a 52-year-old man on suspicion of preventing a lawful and decent burial.
The older woman and man have been bailed until mid-July while the younger woman remains in police custody.
A post-mortem examination on the remains at Great Ormond Street Hospital was inconclusive with regard to the cause of death.
A Metropolitan Police spokesman said: "Further tests will be undertaken and this could take a number of weeks."
He said the death of the child last year was thought at the time not to be suspicious.
He said the case had been referred to its Directorate of Professional Standards (DPS) and also to the Independent Police Complaints Commission (IPCC).