We use these small inexpensive robots to teach robotic to children during our CoderDojo sessions.
See it in action:

https://www.youtube.com/watch?v=LCJ8WDwsZtk

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

Dupont cables

Several lenght M3 screws & nuts