The modular car is based off a normal pullback car except that the body pieces can be removed and replaced. Thus one chassis can be several cars from a pickup truck to a sports car. Along with this the child can also make mashup designs with parts from different cars.
The child can click pieces together onto the chassis with a little force. Along with this it functions as a normal pullback.
The car and body panels would both be made out of hard plastic that would be able to survive being taken apart many many times. Along with that it would need to be able to survive multiple collisions.