The boys love to play with cars, and in this context mother can get 2-3 quiet hours in the day. If daddy will help, then whole evening will be free.

All we need for the base is just an old suitcase.

On tracing paper draw a sketch of the circuit. Black cardboard will be our asphalt. Lawn –green felt. Pavement – black-and-white fabric.
According to pattern on tracing paper cut out pieces of grass between the tracks from felt.

Disposable lawns under the plan, then cut sidewalks from the fabric.

Glue the sidewalk to the grass.