The incident happened as he watched an air show in Suffolk, which had been suffering from heavy rainfall. Two other people were also injured by the lightning strike.
Rex Clarke, head of the team of St John Ambulance volunteers at the event, told AFP: "We got a call that someone had been struck by lightning so we immediately sent our paramedics to the scene, followed by an ambulance.
"Lightning strikes can cause cardiac arrest, but when our volunteers arrived the boy was conscious and breathing.
"This was a minor burn to the boy's shoulder, but he was taken to hospital and is recovering well."
The two other injured people were treated for burns at the scene. It is thought that their umbrellas acted as a conductor for the electricity.