Go to Scratch site (https://scratch.mit.edu/), create an account and show them how to connect blocks together to make the avatar move? Do it together and then check out other people’s works at the same site. You can build upon them.

You don’t need to buy anything.

Install scratch on a desktop or scratch Jr on a tablet. Watch a YouTube video with them making a simple game and implement it together. My kids liked Zoey from Scratch Team channel. We have made a handful of games together and then they kind of take off from there. I'll show them some new things once in awhile or start off a new program with them, but then I'll just leave them to it and they keep going, making it entertaining for themselves.