If a child microphone sounds loud, staticy, or has a lot of background noise it might be the internal microphone that is up to high.
First have child click on the volume icon (bottom right)
Next have them click on the arrow to the right of the sound level.
This will take them to the internal microphone volume setting. They’re setting is probably up the highest, it should be somewhere in the middle of the settings.
I hope this helps.