Smart but bad decision

So I was at the pool with my aunt and my little cousins and one of my cousins was on her period she's like 13/14. So she was wearing a pad and she wanted to get in the pool. And I told her we'll just stick your feet in the water since your wearing the pad and so my aunt was like, you can use a tampon and get in the pool. Which so happen I have them around. So my little cousin uses and come to find out she told her mom. Which is fine, I don't care but I didn't know I stepped a line which showing my cousin something new. Was I wrong for letting my cousin use the tampon?