I guess you could argue that Henry Ford's Quadricycle was the first microcar -- particularly since it is often referred to as the first car.
The little monster was powered by a 2 cylinder 1050 cc engine (driven by belts and chains). It generated 3-4 hp and was able to speed along at 20-25 mph. (Probably as fast as you would want to go, given it's tiller steering and "foot" brake -- putting your foot against the wheel.)
While the engine would put the Quadricycle above the 1000 cc limit of minicars, a quick glance at the car clearly identifies it as one of ours.