The child was travelling with his family from Fair Oaks, Eastleigh, at 8.50pm in a red Nissan Qashqai on the southbound M3.
Police have said that the car was on the slip road at junction 11 when it crashed into the barrier.
The boy, aged 11, was taken to Southampton General Hospital but he later died.
The driver, a 61-year-old man, suffered serious, potentially life changing, injuries.
He was taken to Southampton General Hospital for treatment.
A 48-year-old woman and a 9-year-old girl suffered minor injuries and were also taken to the same hospital.
The family are currently being supported by specialist officers.
Inspector Andy Storey, said: ‘We know the family were travelling from the Basingstoke area so we’d like to appeal to anyone who may have been travelling along this stretch of the motorway prior to the collision, who may have seen the vehicle, to get in touch with us.
‘We would also like to speak to anyone who witnessed the collision. Did you see what happened? Do you have dash cam footage showing the collision or the moments beforehand?’