We did computers and a 10 year old via raspberry pis and Lego. The pis give you a full operating system with WiFi and scratch plus gpio pins, plus a well developed catalogue of peripherals and community. Step one is to blink a LED, step two, drive a hobby servo off a gpio pin. Step three add more servos including continuous rotation ones with wheels. Step four: buy a 3D printer and print specialist Lego bits. All with a sob for a tenner.