The boys were aged 4 and 10. The driver of the car, believed to be the boy's mother, and another female passenger, remain in a stable condition in hospital.
The crash occurred on the northbound carriageway near junction 15 at around 11.25am this morning.
The motorway has now reopened.
More top news
Liverpool Crown Court has heard that a young mother was attacked with a bottle after she tried to stop an argument
Firm is due to be sentenced after death of six year old girl in automatic gate
It may be the season of goodwill but for some Christmas is a lonely and distressing time. Here are some helpful tips on how to cope.