In order to fly, and object must generate lift, be lighter than air or have sufficient velocity such that it resists gravity.
1. Midgets do not generate lift. Their bodies are not aerodynamic lifting surfaces. Their arms are short in relation to their bodies and have a very small surface area. They do not have the leverage to displace a significant volume of air downwards. Their chest muscles are insufficiently small to sustain continual flapping, and their lung capacity is too small to supply the requisite amount of oxygen to their chest muscles.
2. Midgets do not contain any large internal volume capable of being filled with hydrogen/helium gas, thus reducing their apparent mass relative to gravity. They do not float in the air..
3. A midget has a relatively small and compact mass which makes them more suited to be accelerated to high velocity e.g. when fired from an oversized circus cannon. Gravitational forces act on an object over time, so the midget's velocity, although not strictly speaking flight, imparts an inertia to the midget that would allow one to cover a considerable distance before gravity drop impacts It into the ground.