Rephrase prompts
If you feel like you aren’t getting the insights you need because the child doesn’t understand what to do based on your product’s audio or visual prompting (or lack thereof), use the session as an opportunity to explain the instructions in your own words. Note exactly what you said, and whether or not that worked in guiding the kid.
Why this technique
Not only will giving your own guidance and noting exactly what you said help in redesigning your product’s instructions to be understandable, but it will also ensure that kids can proceed in actually playing the game to give you usability insights.