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.
A booster dose is recommended at age 16 years. For teens who receive the first dose at age 13 through 15 years, a booster dose should be administered, preferably at age 16 through 18 years, before the period of increased risk.