Begum ran away from her London home as a schoolgirl after reading about the Islamic State online. She was one of three friends to do so.
Begum, currently lodged at a Syrian detention camp, lost new-born baby Jarrah last month to a chest infection and has repeatedly appealed to be allowed to return to the UK.
Begum's son was born on February 17, days after she was tracked down heavily-pregnant in a refugee camp in Syria.
The 19-year-old IS bride Shamima Begum was stripped of UK citizenship after she flew in 2015 to join the group.
Britain on Wednesday revoked the citizenship of Shamima Begum who had left the United Kingdom four years ago to join the Islamic State in Syria.
Home Secretary Sajid Javid, however, justified the decision, saying that UK cannot accept people who are "full of hate" against Britain and its citizens.
Shamima Begum, who had lost her two children in Syria, recently expressed her wish to return to the UK and said she wanted to raise her new baby in Britain.