Shamima Begum’s child, Jarrah, passed away this week from pneumonia. His death was confirmed by the family’s lawyer.
Begum, 19, was one of three schoolgirls from Bethnal Green in east London who fled Britain for Syria to join Isis in 2015 and was stripped of her British citizenship earlier this month but Jarrah retained his.
In a tweet on Saturday morning, Abbott said: “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.
“Sajid Javid has behaved shamefully.”
Conservative MP Phillip Lee said he was “deeply concerned” by Javid’s decision, which was “driven by a sort of populism”.
“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.
Liberal Democrat home affairs spokesman Ed Davey said the boy will be remembered if courts rule that Javid acted “illegally in making a British citizen stateless”, the Press Association reports.
“Many of us feared this tragic outcome when the Home Secretary washed his hands of Britain’s responsibility for a British citizen and a British baby,” he added.
Kirsty McNeill, a director at Save the Children UK, urged Britain to “take responsibility for their citizens” in Syria.
“It is possible the death of this baby boy and others could have been avoided,” she added.
Begum resurfaced heavily pregnant in a refugee camp in northern Syria last month and spoke of her desire to return to the UK, as the self-styled caliphate collapsed.
She gave birth in a refugee camp in the middle of February, having already lost two children. Her family announced the boy’s birth and said they believed he was “in good health”.
In an earlier interview with the BBC, Begum said: “Losing my children the way I lost them, I don’t want to lose this baby as well and this is really not a place to raise children, this camp.”
Home Secretary Sajid Javid stripped Begum of her British citizenship amid a fierce national debate over whether she should be allowed to return.
Her family, who pledged to appeal against the decision, also wrote to Mr Javid pleading with him to allow a safe passage for the boy to come to the UK.
Last month, Javid confirmed the boy was a British citizen and said he had considered the child’s interest when deciding to revoke Begum’s citizenship.
Following news of the boy’s death, shadow home secretary Diane Abbott criticised Javid’s decision.
She tweeted: “It is against international law to make someone stateless, and now an innocent child has died as a result of a British woman being stripped of her citizenship. This is callous and inhumane.”
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”.
He told BBC’s Newsnight: “The family reached out to the Home Office and requested help. The Home Office sent a reply and said ‘You’ve come to the wrong department, you need to speak to Foreign and Commonwealth Office’. There was no attempt to help by the Home Office.
“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.
“We failed to safeguard her and now we have failed, as a country, to safeguard a child – a totally innocent British subject.”
He added that he believed the decision regarding Begum’s citizenship should be “urgently” reviewed.
Javid, when asked whether there was any plan for 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 spokesman said: “The death of any child is tragic and deeply distressing for the family.
“The Foreign and Commonwealth Office has consistently advised against travel to 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.”