The accusation comes as lawyers for the Begum family announced the death of Jarrah on Friday – three weeks after the home secretary revoked his mother’s British citizenship over links to the terror group Isis.
Ms Begum, 19, resurfaced last month four years after joining the self-styled caliphate as a 15-year-old. Heavily pregnant in a refugee camp in Northern Syria, she spoke of her desire to return to the UK.
On 17 February, her family announced the boy’s birth and said they believed he was in “good health”.
But on Friday the death of the child was confirmed by Ms Begum’s family lawyer Tasnime Ankunjee. “He was a British citizen,” he had earlier posted on social media.
Ms Abbott, the shadow home secretary, said the death of Jarrah was a “stain on the conscience of this government”, adding: “It is against international law to make someone stateless. And to leave a vulnerable young woman and an innocent child in a refugee camp, where we know infant mortality to be high, is morally reprehensible.”
She continued: “Whenever there are reasonable grounds to suspect that someone who is entitled to return to this country has either committed or facilitated acts of terrorism, they should be fully investigated and where appropriate prosecuted. In an effort to appease the right-wing press, the home secretary would not even grant Shamima this.
“The home secretary failed this British child and he has a lot to answer for.”
Mr Javid also faced criticism from his Conservative colleague Phillip Lee MP, who said he was “deeply concerned” at the decision to strip Ms Begum of her British citizenship last month in a move that triggered a furious row.
“Clearly Shamima Begum holds abhorrent views and to want to join Islamic State is beyond all comprehension, but she was a child, a product of our society,” he told BBC Radio 4’s Today programme.
He added: “I think we had a moral responsibility to her and indeed to her baby. That is why at the time I was just troubled by the decision.
“It seemed to be driven by a sort of populism, not any principle I recognise.”
Dal Babu – a former Metropolitan Police chief superintendent and friend of the Begum family – described it as an “entirely avoidable death of a British citizen”.
“What we have here is a totally innocent child, whatever you may think of Shamima’s shortcomings, the mistakes she made as a 15-year-old child when she was groomed on our watch,” he added.
“We failed to safeguard her and now we have failed, as a country, to safeguard a child – a totally innocent British subject.”
But the Conservative Party chairman Brandon Lewis defended Mr Javid’s decision to strip Ms Begum of her British citizenship in February.
“The loss of any life of any child is absolutely tragic and is a very clear reminder – this whole case – of the danger of travelling out to that area and getting involved,” Mr Lewis told the BBC on Saturday.
“The home secretary will have had advice and I know he made a decision based on what is in the national interest and the security of people here in the UK.
This week a British baby died from pneumonia in a Syrian refugee camp. A tragedy that might have been avoided. If the mother & baby had been brought home, the mother Shamima Begum would have faced British justice, but the baby might have lived. @sajidjavid has behaved shamefully pic.twitter.com/LNU14EBTfE
— Diane Abbott (@HackneyAbbott)
“There is no question that the duty of a home secretary in this country is to keep British people safe.”
Mr Javid, when asked whether there was any plan for Ms Begum’s son, had previously told the Commons’ Home Affairs Committee it would be “incredibly difficult” for the government to facilitate the return of a child from Syria.
“If it is possible somehow for a British child to be brought to a place where there is a British consular presence, the closest place – it might be Turkey for example – in those circumstances I guess potentially it is possible to arrange for some sort of help with the consent of the parent,” he added.
“Inside Syria, whether in a camp or maybe somewhere else, there is no British consular presence.”
A government spokesperson said: “The death of any child is tragic and deeply distressing for the family. The Foreign and Commonwealth Office has consistently advised against travel in Syria since April 2011.
“The government will continue to do whatever we can to prevent people from being drawn into terrorism and travelling to dangerous conflict zones.”