(Kids? On tribe? 18+ only...it's right there in the agreement when you sign up. Grown ups play here. If they're too young to handle mature content, then they shouldn't be here. Just sayin'...)

There's not really all that much you can do about the related tribes.
You could try inviting members that don't have any mature tribes in their list. That may bump some of your tribes out of the 'related tribes' section.
You could leave the *mature* tribes until your membership is large enough that the 'related tribes' is no longer based on your tribe list, then rejoin the ones you left.

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