A mother whose baby son died from an overdose of the heroin substitute methadone has pleaded guilty to causing his manslaughter by gross negligence.
Fennelly and Mr Bate had both faced manslaughter charges
Mitchell Bate, aged 22 months, was found dead at home in Rodney Street, Hartlepool, in September 2005.
Gemma Fennelly, 24, of Edinburgh Grove, had originally been accused of giving her son the drug to keep him quiet.
Mitchell's father, Mark Bate, 34, was cleared. Fennelly will be sentenced at Teesside Crown Court on 3 May.
Fennelly admitted "allowing and/or failing to prevent" her son from swallowing a lethal dose of methadone.
She and Mr Bate originally stood trial in October, but proceedings were halted to allow further forensic tests to be carried out.
On Wednesday, Andrew Robertson QC, prosecuting, said: "Considering the case as a whole, we do not allege wickedness on the part of this defendant.
"It is a tragedy, but it is a criminal act, given her plea. After some consideration it would not be appropriate to prosecute Mark Bate."
In October, the court was told that Mitchell, whose parents were both said to be heroin addicts, was given methadone to keep him quiet.
During those proceedings, the prosecution said traces of heroin and cocaine were found in hair samples taken from the baby after his death.
The court was also told that Mitchell's parents kept their prescribed medication in a locked metal box on a kitchen shelf he would barely have been able to reach.
Mr Robertson said blood samples proved Mitchell had had regular doses over a protracted period.
Granting Fennelly bail, the Recorder of Middlesbrough Judge Peter Fox said: "You should understand my giving you bail now is no indication whatsoever of your sentence on 3 May."