A post-mortem showed Kieron suffered a spinal fracture and a brain injury in the last three weeks of his life
A man who inflicted "catastrophic" brain injuries on his partner's 22-month-old boy in a fit of temper has been jailed for eight years.
At Birmingham Crown Court, Craig Lewis, 32, admitted the manslaughter of Kieron Barley, who was violently shaken.
Lewis also admitted inflicting harm in an assault two weeks before the fatal 2011 attack in Birmingham.
Kieron's mother, Louise Barley, 26, admitted child cruelty and was jailed for 15 months.
A post-mortem examination showed Kieron had suffered a spinal fracture and brain injury in the last three weeks of his life.
West Midlands Police said Lewis and Barley lied about how the injuries were sustained after Kieron's death in June 2011.
In May 2012, the pair were arrested on suspicion of his murder, but the charge was later changed.
Police said Lewis told officers Kieron had fallen forward while attempting to walk, and Barley said she had witnessed the incident, although it was proved she had been out at the time.
Craig Lewis attacked Kieron after losing his temper, police said
Louise Barley lied to police about Kieron's injuries, the court heard
An MRI scan of Kieron's body found he had suffered subdural and retinal haemorrhages likely to have been caused by shaking or an assault.
Lewis had told probation officers his conduct was the result of "underlying stresses coming to a head".
In sentencing, Judge William Davis QC told Lewis he had not "fully explained" the reasons for his actions.
"The trigger appears to have been relatively minor and he reacted with considerable violence towards a young and vulnerable child," he said.
"I am asked to consider you are now remorseful and contrite, but I have difficulty in accepting that proposition."
Det Ch Insp Dawn Miskella said the case was "tragic and deeply upsetting".
"Young Kieron lost his life after Lewis admitted losing his temper on two occasions and assaulting him," she said.
"Kieron was sadly let down by those who should have been caring for him."
A serious case review has started into the involvement of various agencies with Kieron and the defendants.
Jane Held, chairwoman of the Birmingham Safeguarding Children Board, said the findings would be published "as soon as possible" following the end of legal proceedings.
It emerged during the case Kieron had been admitted to Birmingham Children's Hospital following the first of the two incidents in May 2011.
A spokeswoman for Birmingham Children's Hospital said it had completed an internal review and submitted its findings for inclusion in the case review.