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.
Booster seats are extremely safe, but for older children. Booster seat companies like to advertise their booster seats for use at 3 years old and 30 lbs. This is a terrible recommendation. At 3 years old, your child could die in a booster seat because their bodies cannot take the force of a 3 point belt.