Johnson’s pledge comes in the wake of nationwide shock over the murder of Arthur Labinjo-Hughes, six, who died at the hands of his stepmother Emma Tustin in June last year.
Arthur was left with a fatal brain injury after Tustin assaulted him while she was supposed to be looking after him.
The youngster, whose body was covered in 130 bruises, died in hospital the next day.
On Friday (December 3), Emma Tustin, 32, was found guilty of murder and jailed for a minimum term of 29 years. Arthur’s father, Thomas Hughes, 29, was jailed for 21 years for manslaughter.
However, the Attorney General’s Office (AGO) has now confirmed that the sentences are to be reviewed to ‘determine whether they were too low’.
And Mr Johnson told The Sun he supported the idea that the killers would remain in prison for the rest of their lives.
He said: “Anyone who plans then carries out the murder of a child should never be released from prison.
“So we’re toughening the law to make whole-life orders the starting point for such abhorrent crimes.”
The AGO has 28 days from the date of sentence to review a case. It must assess whether the case falls under the Unduly Lenient Sentence (ULS) scheme.
Then, the AGO must make a decision as to whether to refer a sentence to the Court of Appeal. The Court of Appeal then makes the decision about the sentence.
Though the new laws highlighted by Johnson would mean tougher sentences for child killers, it would not necessarily apply to those already jailed, like Sarah Barrass and Brandon Machin.
Sarah Barrass and Brandon Machin were jailed for life and ordered to serve a minimum of 35 years behind bars last November. They admitted to killing their two sons Blake and Tristan at their Shiregreen house in 2019.
Barrass and Machin could still be released once their minimum terms have been served.
The killings shocked Sheffield, as the extent of the evil incestuous couple’s crimes were revealed.
The house in Shiregreen where the crimes took place has been demolished to make way for a memorial to the victims.