Ask HN: Terminal-Based Games for Kids

I don't want to make it hard but accidentally I've found that linux terminal-based games/tools are just awesome for my kids too. They now can log in to the machine themselves, start the shell and there are already two fun things they can spend a lot of time with

* ponysay * cowsay

Are there any more games/tools for kids which are based on terminal?

To be honest, I can give them xfce/gui access, but then there are a ton of things they/I have to worry.

Thanks