We use these small inexpensive robots to teach robotic to children during our CoderDojo sessions.
See it in action:
The device is fully programmable with mBlock suite (very user friendly).
What do you need:
1x Set of printed parts (attached)
1x Small turning wheel (https://www.bricoman.it/n/ferramenta/mobili/ruote/girevoli/ruota-sferica-26mm-portata-30kg-polipropilene/10008186/)
2x Smart car TT gearboxes & wheels (https://www.aliexpress.com/wholesale?catId=0&SearchText=tt+gearbox)
1x Arduino uno (or clone)
1x HC-SR04 ultrasonic sensor (https://www.aliexpress.com/wholesale?catId=0&SearchText=HCSR04)
1x L298 dual bridge (https://www.aliexpress.com/wholesale?catId=0&SearchText=L298+board)
1x Battery holder
1x on/off switch
1x Jack power connector
Wires for motor & power cabling
Several lenght M3 screws & nuts