Tareena Shakil, 26, was pictured with assault weapons during nearly three months in the organisation’s stronghold of Raqqa. She dressed her son in clothes bearing its insignia.
The prosecution claimed her intention had been to have him trained as a jihadi fighter.
She was also convicted of encouraging terrorism on social media following a trial at Birmingham Crown Court.
She is thought to be the first British woman to be convicted of terrorism offences after returning from Syria.
Shakil began expressing support for IS on Facebook in the summer of 2014, after communicating online with a jihadi fighter in Syria.
She changed her profile picture to the IS flag and wrote messages supporting the group. In one, she said that people who do not like what is happening in Syria should “take to arms and not the keyboard.”
In October 2014, she flew to Turkey with her son, before crossing the border into Syria, leaving farewell notes for her family at her home in Birmingham.
She claimed in court she had travelled there to seek “a pure Muslim life” under Sharia law, and had not known the true nature of IS until she arrived.
Shakil said she had been unhappy in Raqqa, despite sending messages home on Christmas Eve saying, “I’m not coming back, I’m happy here, I love it here.” She claimed her communications were being monitored by minders.
She described her eventual escape from IS territory in early January 2015, claiming she bribed a taxi driver to take her to the border, before dashing the last 1km past armed fighters and across barbed wire with her son in her arms.
She was picked up by a Turkish military patrol and arrested on her return to the UK.
Giving evidence during the trial, she told the jury she had provided intelligence to MI5 and offered to help in de-radicalisation programmes following her arrest.
Her child, who cannot be identified, is now in care.
Assistant Chief Constable Marcus Beale, from West Midlands Police, said: “They are a dangerous, dangerous organisation and anyone that is a member of that organisation poses a threat to the UK and to other western countries. I really welcome the conviction.”