Bus operators will often find it economical to convert retired buses to use as permanent training buses for driver training, rather than taking a regular service bus out of use. Some large operators also converted retired buses into tow bus vehicles, to act as tow trucks.
Explain to an 8 year old child that is not yet 49 tall that the safety equipment built into the vehicle is for adults  not children, and a child needs to continue to use the proper equipment (booster seat) so that the adult equipment will fit, and be able to protect, their bodies in the event of a crash.
Age is a key factor as there is no way a 2.5 year old is mature enough to sit still in a booster seat. Please note that kids should be AT LEAST 4y AND AT LEAST 40 pounds AND mature enough to sit properly (no slouching, no leaning over, no playing with the shoulder belt, etc) before riding in a booster. Your 2.5 year old needs to ride in a 5 point harness.