The incident took place just after 8 a.m. on Thursday in Halton Hills, Ont. (at Sixth Line and Steeles Ave).
Halton Regional Police say all children who were on the bus are conscious and have been taken off the vehicle.
Tanker truck rear-ended bus
Sgt. Barry Malciw says it appears the tanker truck rear-ended the school bus. He says the truck was carrying home-heating fuel, but there doesn't appear to have been a spill.
The children were treated by paramedics from Peel and Halton region.
Some children were seriously injured
Peel Region paramedics say two of the children have been taken to a hospital in Hamilton with serious but non life-threatening injuries.
Halton Region paramedics say the remaining five children and the bus driver were taken to a hospital in Milton, Ont., with "minor to moderate'' injuries.
Photographs from the scene show the back of the school bus partially caved in and damage to the front end of the tanker truck.
Police say it's too early to say if charges will be laid. A collision reconstruction unit is investigating the incident.