Only one of my headphones is working. Help?

My niece has some kind of addiction of putting headphones into her mouth and now after seeing her putting one of my headphones into her mouth while my phone was charging, I grabbed my headphones and checked if they were working but only the one she didn't put into her mouth was working. I've searched on YouTube and they said to blow gently and softly into the line on the outside of the headphones to make it work but nothing worked after about 5 attempts. i can only hear a tiny bit when I put the broken one into my ear alone it's so quiet but you can still hear it but not as clearly. If i put both of them into my ears, I can only hear loud and clearly out of the good one