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
The woman is described as being around 50 years old with short spikey purple hair.
A man has been arrested under the Psychoactive Substances Act 2016, less than 24 hours after it came into force, banning 'legal highs'.
Compared to the last few days, it looks like an improvement over the next few days. Some uncertainty about Monday though.....