The Attorney General has decided against referring the sentences handed down in the Baby P case to the Court of Appeal, she said today.
Baroness Scotland announced last month that she was considering whether the jail terms given to the three people convicted over the little boy's death were "unduly lenient".
But she concluded today that there was "no realistic prospect" of the Court of Appeal increasing their sentences.
Baby Peter was 17 months old when he was found dead in a blood-spattered cot in Haringey, north London, in August 2007 having suffered a broken back and fractured ribs.
His mother, 27, was given an indefinite sentence with a minimum term of five years at the Old Bailey last month after pleading guilty to causing or allowing her son's death.
Judge Stephen Kramer described her as "manipulative" and "calculating" while rejecting her claim that she was too naive to realise what was going on in her house.
Her boyfriend, 32, was jailed for life with a minimum of 10 years for raping a two-year-old girl.
He was also given a 12-year term to run concurrently for his "major role" in Peter's death.
The couple's lodger, Jason Owen, 37, of Bromley, south-east London, received an indefinite sentence with a minimum term of three years for failing to take steps to save the little boy.
Baroness Scotland reviewed the case papers, the law and the relevant sentencing guidelines before deciding against referring their tariffs to the Court of Appeal.
She said: "It was clear to me that the judge, who had heard all of the evidence, fully appreciated the gravity of these terrible offences and took into account all of the relevant factors...
"I believe that the sentences fall within the range that it was reasonable for the judge to have imposed and there is no realistic prospect that the Court of Appeal would increase the sentences if I referred them."
The Attorney General said the life and indefinite sentences handed down by the judge were "entirely merited".
She stressed that the three defendants would only be released if and when they no longer presented a risk to the public, and children in particular.
"Those closest to the victims deserve our utmost sympathy and support," she said.
"This is a shocking and distressing case which has given rise to great family pain and anguish and a proper degree of public anger and outrage."
Baroness Scotland's decision came as it emerged that the mother's boyfriend has launched an attempt to overturn his convictions for rape and causing or allowing Peter's death.
His lawyers have now lodged papers appealing against both convictions and both sentences with the Court of Appeal, a legal source confirmed.