I would recommend installing Scratch[1] - it's a programming language designed for kids from 8yrs old onwards. I would recommend pairing it with a Raspberry Pi, as you can do fun real-world physical stuff with using Scratch, and I think kids can find that very interesting. Eg, start with a simple program to turn LED lights on and off, programming buttons, playing sounds etc. Eventually this could lead to making simple games or other programs. Regardless, would highly recommend getting a Raspberry Pi as its just so much fun using it to interact with the physical world and getting to learn actual electronics.
[1] https://scratch.mit.edu/parents/