You've certainly identified a number of the operational considerations that have to be looked at as part of the mandate of the school bus task force. As Kevin noted, and as you noted, the size of the children, accounting for the nature of children in school buses, can range from very small children who would be required to have booster seats, which would still be a requirement, to school children who are virtually adult-sized. Being able to account for the varying adjustments and the operational considerations is a key component of this.
The task force is also looking at a number of other complicating factors, such as the requirement to be able to quickly unfasten seat belts in the event of an emergency, and to be able to monitor and ensure that the seat belts are always correctly worn by all occupants all the time. These are important safety considerations to account for, to ensure that the use of the seat belts doesn't compromise the other safety features available on the school bus.
The task force is developing operational guidelines to be able to potentially support the use of seat belts in the event that we go in that direction.