In the Solar System activity in https://gcompris.net/download/qt/linux/beta/gcompris-qt-1.0-beta-Linux64.sh, all the input comes via the keyboard. The up and down arrow keys control vertical thrust. The left and right arrow keys control either horizontal thrust (levels 1 - 7) or rotation (levels 8 - 14). When a level is over, the next one doesn't begin until the "OK" button is clicked //with the mouse//.
I think it would be better if it were possible to "press" the "OK" button without needing to use the mouse. I had three thoughts about how to achieve this.
1. Bind the "Enter" key to the "OK" button.
2. Bind all four arrow keys to the "OK" button.
3. Bind all keys other than those already in use (like "ESC") to the "OK" button.
I like 2 the best. My hand is already on the arrow keys from the previous level, and it is very natural for the user to push an arrow key potentially thinking that the next level has already started. The "OK" button is like a modal popup but doesn't take up much of the screen, so it is easy to miss it. This is especially true in the levels with low acceleration since the initial state of those levels at the first few seconds are very similar (since the velocity remains so low).
Could also do both 1 and 2 to increase the chance that the user discovers this quality of life improvement. Option 3 significantly increases this chance, but as a programmer, I am worried that some key binding might be stolen from some other behavior (like how binding "ESC" to the "OK" button would steal this key from its current behavior of exiting the activity).