The incident happened near The Gore Road, north of Old Church Road.
The bus is now tilting sideways into the ditch and police have requested a tow.
All children are outside with the driver of the vehicle.
The OPP Central Region tweeted that no injuries were reported.
Drivers are advised to avoid the area as the bus moves away, police said.
#CaledonOPP is currently on stage at The Gore north of Old Church at @YourCaledon for a school bus in the moat. Students were on board, but fortunately there were no injuries. Avoid avoiding as the bus moves away. ^ jb pic.twitter.com/9rVqWgDP10
– OPP Central Region (@OPP_CR) June 29, 2022