My cousin saw my thong, should I be worried?

So I was babysitting my cousin who is a 12 year old boy and his 10 year old sister. I was playing around on the floor with his sister when I noticed my cousin sitting on the couch staring at me. I reached around and noticed my thong was showing out of my pajamas. Should I let his parents know that he was staring at my thong? is this normal behavior for a boy his age? Should I have a talk with him? Thanks for any advice.
My cousin saw my thong, should I be worried?
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