If you still have the cars, depending on condition, if sold online, could pay for a modern sturdy, lower cost set for the grandkids to crash about on. Generally the more detailed cars are more fragile and expensive. If you buy such a set without selling the old cars, suggest strongly keeping them as shelf queens. If you decide to use the old cars on a track, you need to check if the axels ,motor and gears still turn and lightly oil all moving parts. Clean guide brushes and connect 9 volt battery to check wiring and motor. Tires will need replacing ( check dealers on line ) , since they have turned to stone or broken off. The plastic bodies will be very fragile.