A camera outside Abington Supermarket filmed the moment an electrical fault caused the explosion in the pavement next to a cashpoint being used by the family.
The force of the blast ripped part of the newsagent’s shop sign down, which narrowly avoided colliding with the head of the young boy.
Emergency services were called out to the incident shortly after 8.00 a.m. on Tuesday last week and the mother was treated by the ambulance service.
An East Midlands Ambulance Service spokesman said: “An ambulance attended to treat a woman who had been walking in the area with two children when the cover flew into the air, but there were no serious injuries.”
A spokesman for Northamptonshire Fire Service said the cause of the explosion was an electrical fault in an underground box.
A large trench was built outside Abington Supermarket to allow workers from Western Power to fix the junction box.
The sound of the explosion was heard by residents in the town centre and surrounding area.