This project was the simplest, which I did to demonstrate to a primary school class, how easy it is to create robots.
It is simply a toy doll of Batgirl whose arm is connected by a stiff wire to a servo motor controlled by an Arduino microcontroller.
This is the Arduino code
All it does is to move the arm of Batgirl up and down, over and over again. Simples yes ? But ask someone if they think they can do this and maybe you get a negative answer. This is not difficult. Then you can introduce other control criteria, e.g. time, info from other sensors etc.
Spark their imagination.