The pilot reported that, during the initial climb, he inadvertently switched off the engine magnetos with his coat sleeve while using the trim handle causing the airplane’s engine to shut down; the switches were located on the left side of the cabin. The pilot realized the problem, but, due to the airplane's low altitude, he decided to land instead of trying to restart the engine and climb over obstacles at the end of the airstrip. The airplane touched down in an area of tree stumps and brush, sustaining substantial damage to the wings and fuselage. A postaccident examination of the magneto switches on the accident airplane and other like models revealed that a pilot's coat sleeve can contact and move the guarded magneto switches. The pilot stated that the accident could have been prevented by moving the magneto switches to the instrument panel.