Hello. I am disassembling a small RF controlled toy car. I'm down to examining the circuity now and there are two motors inside the toy. I see both motors have 100nF capacitors across the negative and positive leads of the motor.

I understand that capacitors are open for DC and the motors are only ON or OFF so can somebody explain to me why they are there?

 

they are there to provide a low impedance path for the sparks occurring on the brushes, so the RC control channel isn't swamped by the noise.. They're just a short-circuit path for the spark energy.