A coach carrying 53 adults and children from the West Midlands on a day-trip to the seaside overturned in a ditch off the M5 in Gloucestershire.
The crash happened just before 10:00 BST close to junction 13 for Stroud.
Five adults and one child were injured, a South West Ambulance Service spokesman said. All of them were said to have minor injuries.
Police said seatbelts on the coach may have helped reduce the number of casualties.
The injured child was taken to Bristol Children's Hospital, the adults to Southmead Hospital.
The coach driver had a suspected back injury.
The Confederation of Passenger Transport said it had been told three of the six people taken to hospital had been discharged.
The M5 fully reopened at about 15.30 BST, five and a half hours after the coach overturned.
Ch Insp Yan Georgiou from Gloucestershire Police said collision experts were investigating the circumstances.
"What's remarkable is the number of casualties and a really important safety message is starting to emerge.
"The passengers were wearing seat belts, without them this could have been a very different picture," he said.
The coach was operated by Stourbridge-based Prospect Coaches and was taking the group to Weston-super-Mare.
The Confederation of Passenger Transport (CPT), which represents operators of UK buses, said it understood it was one of four coaches making the same journey.
Passengers were collected from a children's centre in West Bromwich at 08:30 BST.
A spokesperson from the charity Action for Children, which chartered the coach, said: "I can confirm that a road accident involving children and staff from an Action for Children service in Sandwell has taken place in Stroud.
"Until the full facts are known I cannot comment further."
No other vehicles were involved in the crash.