Elvis Lee, 34, was found guilty yesterday of murdering Tyler Whelan, five.
Lee admitted he kicked and bit Tyler on the day of his death but denied murder.
The kick was so hard that Tyler flew two feet through the air hitting a door at his home in Sheepwalk, Paston, near Peterborough, rupturing his abdomen and slowly killing him.
At Cambridge Crown Court today, Mr Justice Nicol sentenced him to life with a minimum tariff of 17 and a half years.
He said: ''Tyler had been left in your care while his mother took two other children to school.
''His young life was cut tragically short. This has been a tragedy for his father, his mother and the rest of the family.
''Tyler was particularly vulnerable because of his age. He was only half your height and a quarter of your weight.
''I entertain the lingering suspicion you inflicted more blows than you have admitted and that may have been the reason Tyler said nothing to his mother when she returned.''
The boy's mother, Stephanie Whelan, 27, was found guilty of allowing the boy's death. She will be sentenced next month.
A report published after the conviction found that key opportunities to protect Tyler were missed by authorities tasked with his care.
It acknowledged that previous incidents in which the boy was hurt had been ''seen in isolation'' with ''minimal attempts to link concerning patterns of injuries''.
Michael Borrelli QC, mitigating, said Lee's attack on Tyler on March 7 last year was not pre-meditated and was instead a loss of temper and ''act of spite''.
He said: ''My client was himself the victim of considerable violence as a child.
''He lacked a real appreciation as to the consequences of what he did because, despite the treatment he himself had been the victim of, he had never suffered serious injury.''
The trial heard evidence that Tyler suffered a number of ''non-accidental'' injuries in the year before his death.
But Mr Borrelli said his client had been cleared of cruelty and neglect allegations and should be sentenced on the basis that this was an isolated attack.
Whelan, of Sheepwalk, Paston, but originally from Wigan, and Lee, of Crabtree, Paston, were each cleared of two counts of cruelty or neglect relating to their failure to seek prompt medical attention on previous occasions.
A serious case review, compiled by the Peterborough Safeguarding Children Board and published after the verdict at Cambridge Crown Court, acknowledged failings by the organisations responsible for his care, including Peterborough Children's Services.
The report concluded that it was impossible to say that, had there been greater intervention, the tragedy would have been prevented.
But the report said: "Whilst it would be very challenging to state with any conviction that the subject's (Tyler's) death was either predictable or preventable, there were certainly numerous missed opportunities when interventions should have been more rigorous and incisive on clear occasions when there were concerns about his safety at home.
"Additionally, there were some occasions when initiatives were not taken to assess the levels of risk to the subject when there was a procedural requirement to have done so.
"Even if any of the missed assessment opportunities had in fact been taken and completed in line with procedures, it could still not be said with any certainty that they would have made a difference to the eventual tragic outcome."
Superintendent Simon Megicks, from Cambridgeshire Police, said: "This was a wicked crime in which an innocent five-year-old was murdered by a person who should have been looking after him.
"Lee is a controlling and violent man who lost his temper and inflicted fatal injuries to Tyler.
"Whelan has been found to have allowed his death following these fatal injuries - Tyler deserved more from his mother.
"Every child has the right to be protected and feel safe in their own home and it is a parent's responsibility to ensure this is the case."