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.
How old will my child need to be to use this new type of backless booster? There's no exact age - suitability is measured by height or weight of your child. But to give you an idea of age, 125cm tall or 22kg in weight is approximately the size of a 7-year-old child - although of course children vary enormously, so it's only a rough guideline.