Pupils were heading to Our Lady and St Patrick’s High School from Balloch and Old Bonhill when the incident happened at 8.40 am on Wednesday on Renton Road in Dumbarton.
The male driver of the car involved was cut free from his vehicle and airlifted to the Queen Elizabeth University Hospital in Glasgow.
Two adults and 21 children were also taken to Queen Elizabeth University Hospital and the Royal Alexandria Hospital in Renfrewshire, the Scottish Ambulance Service confirmed.
A spokeswoman for West Dunbartonshire Council said: “All affected parents and carers have been informed.
“Parents needing any information should contact the school.
“Further information will be provided as soon as it’s available.”
The road between Dalreoch station and the slip road to the A82 has been closed to traffic.