Kevin Banks, a building contractor from Stroud, employed the boy to work for him on a site on Rodborough Common.
It is illegal for children who are still of compulsory school age to work on construction sites.
Gloucester Magistrates’ Court heard how on 13 April 2010, the boy overturned the one-tonne dumper truck when driving down a slope. He was not wearing a seatbelt and suffered serious leg and foot injuries.
A Health and Safety Executive investigation found Banks had failed to properly plan, manage and monitor the work to ensure the boy and others were not put at risk.
Other untrained employees had also driven the dumper truck, often without wearing seatbelts, on some steep slopes.
After the hearing, Sue Adsett, HSE inspector, said: “Children and construction work do not mix. As this incident shows, construction sites can be very dangerous, and children tend to have less experience and less awareness of what could go wrong.
“Furthermore, anyone operating site dumpers should prove their competence to do so by holding an industry-recognised CPCS driver’s card.”
Kevin Banks, trading as KB Building Services, pleaded guilty to failing to comply with section 13(2) of the Construction (Design and Management) Regulations 2007 and was fined £2,000 and ordered to pay costs of £4,052.