If you find the cheerson CX-10 already small, recently picoquadcopters have been announced. They are 1/3 smaller than nanos !!!!
For example, this D1 model
Item name: D1 Drone Mini RC Quadcopter
Gyro: 6 axis
Lipo-battery: 3.7V 80mAh(Included)
Remote battery: 3 x AAA dry battery(Not included)
Charging time: 30mins
Flying time: 5-7mins
R/C distance: about 25m
Flying distance: about 20m
Mode: Mode 1(Right hand throttle),Mode 2(Left hand throttle)
3D rollover,hovering at any angle
With Headless Mode,no need to adjust the position of aircraft before flying .
4 channel which can fly forward/backward,ascend/descend,turn left/turn right,360-degree rotation.
It has 6-axis gyro which can have more stable flying and be easy to control.
Lightweight airframe with nice durability.
1 x D1 Mini RC Quadcopter
1 x 3.7V 80mAh battery
1 x Transmitter
1 x USB cable
4 x Propeller
1 x Manual
In fact, the model is sold with different name, i.e. Floureon FX-10 or now rebranded by Cheerson as CX-star