How do I convince my nieces?

My nieces have just started high school, and have become interested in boys. They are trying to get big asses because they say all guys love them. I keep tellin them they're wrong, but they won't believe me. Some guys do love big asses, but not all of them. How can I convince them that not all guys love big asses?

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I am not their biological uncle, if that matters.
How do I convince my nieces?
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