Hairdresser Adrian Hoare, 24, from Gravesend in Kent, was found guilty of putting her son Alfie into harm’s way by placing him into the footwell of an Audi convertible.
She has been jailed for two years and nine months over his tragic death.
Her boyfriend Stephen Waterson, 25, from Croydon, adopted son of former Government Minister Nigel Waterson, was accused of squashing Alfie by reversing his car seat into him.
The Old Bailey had heard how Alfie screamed for his “mummy” but Hoare just slapped him and told him to “shut up”
By the time they arrived at Waterson’s home in Croydon, south London, the boy had collapsed and stopped breathing.
As medics desperately tried to revive him, Hoare spun a web of lies, claiming she had been in a taxi.
“There was an element of deliberate disregard for Alfie’s welfare.”
Mr Justice Kerr
Alfie, nicknamed “Little Tarzan” by his mum, died from crush asphyxia three days later.
Hoare was found guilty of child cruelty and assaulting Emilie Williams, who was in the car when Alfie was fatally hurt.
Hoare had also admitted plotting to pervert the course of justice in the wake of her son’s death.
Waterson faces a retrial for Alfie’s manslaughter in September.
Mitigating for Hoare, Katy Thorne QC said Alfie had been a “happy child” and there were no issues of neglect before the events leading to his death.
She told the court: “Ms Hoare has been hugely affected by Alfie’s death, not least because she feels a huge amount of guilt over it.
“Ms Hoare is deeply remorseful of what happened in that car that night.”
Ms Thorne said that, since her conviction, Hoare had co-operated with police and agreed to “do the right thing” and give evidence in Waterson’s upcoming trial.
Mr Justice Kerr jailed Hoare for two years for cruelty plus eight months for perverting the course of justice and one month for assault, all consecutive.
He told her: “This is a very sad case. You intended no harm to Alfie.
“You put him in danger by allowing him to travel in the footwell of the car.
“There was an element of deliberate disregard for Alfie’s welfare.
“I cannot ignore your own admission that you had allowed him to travel in the footwell many times.”
He said Hoare failed to tell paramedics and doctors what happened and should have disclosed “anything that might have helped him”.
“I accept and bear in mind you lost Alfie, your only child.
“That is punishment already.
“I accept you are remorseful although it did not show very much because you were numb in your trial.”