Over the weekend I found myself coding a JS game for my kids. The game is very straightforward a word scrambler for kids at the ages of 6-9.
After finishing the first version, I sent the game to some colleagues to get feedback, and here are the things I learned:

• plan the game before you start coding. Try to imagine the game flow, write the scenes on paper, and try to understand the game as it is.
• Big control: while coding, always test your code, and see if things are working as expected.
• get your kid's opinion, about everything, colors, text, words, settings.
• feedback is important, while they are playing the game, kids, especially young ones, must have some kind of feedback, preferably visual.
• hints and help: following the previous point, they sometimes need help. Adding some kind of help/clue after 2-3 failures is a must, otherwise, they will feel frustrated.