A toy prime mover has a hollow housing provided with a spring windup mechanism which can be wound up by a crank at the back of the housing and which has output shafts at the front of the housing, at the sides of the housing and at the bottom of the housing. Ground-engaging drive wheels are connected to the output at the bottom of the housing. A support plate can be connected to each of the shoulder joints surrounding each of the output members at the sides of the housing and each such support plate can carry a pair of large-diameter ground-engaging wheels that are driven via gears from the output member of the shoulder in order to allow the prime mover to displace itself over relatively rough terrain. A trailer may be connected to the back of the prime mover and has a ground-engaging steering wheel mounted on an arm carrying at its end a magnet. A wand also provided with a magnet can magnetically swing this arm to steer the prime mover without touching it. The output member at the front of the housing may be connected via a coil spring to the similar output member at the front of another such prime mover and the shoulder joints may be provided wit ground-engaging support arms so that the two devices can be wound up and allowed to wrestle with each other.