Hi! I understand that you're using JusTalk Kids to talk while playing Roblox on your Kindle running Android 11, but you can't hear your niece. Let's try to get this sorted out together.

First, just to make sure we're on the same page:
- Can you confirm if the microphone and speaker work fine when you use JusTalk Kids without playing Roblox?
- Also, do you have any other audio apps running at the same time?
- Are you using headphones or the device's built-in speakers?

This helps me figure out if it's a permissions issue, a conflict between apps, or something else.

Meanwhile, here are some steps to try:

1. Check App Permissions:
- Go to your Kindle's Settings > Apps > JusTalk Kids > Permissions and make sure the microphone and speaker permissions are enabled.
- Since you're using Android 11, permissions might reset or restrict in the background if the app hasn't been used recently.

2. Close Other Apps Using Audio:
- Sometimes, Roblox and JusTalk Kids might conflict if both try to access the microphone or speaker simultaneously.
- Try closing Roblox completely, then test JusTalk Kids to see if audio works fine. Then, reopen Roblox and try again.

3. Restart Your Device:
- A simple restart can often resolve resource conflicts between apps.

4. Check JusTalk Kids Audio Settings:
- Open JusTalk Kids during a call, and ensure the volume is turned up and any mute buttons are off.
- Also, sometimes there is an option to select the audio output (speakers or headphones). Make sure it corresponds to your setup.

5. Update Both Apps:
- Check if you have the latest versions of both JusTalk Kids and Roblox installed via the Amazon app store.
- Updated versions fix many issues, including audio conflicts.

6. Try Using Headphones:
- If you aren't already, using headphones might isolate audio and improve call sound quality during gameplay.

If you’ve already tried these or if the problem persists, please let me know what steps you’ve taken and how the apps behave separately and together, so we can dig deeper.

Are you comfortable trying these? Let me know how it goes!