Okay kiddo, have you ever seen a balloon? Sometimes when we try to blow up a balloon, it doesn't get as big as we want it to. That's because the air can't get through to fill it up all the way.
Well, sometimes grown-ups have a similar problem with their "balloons," except it's not really a balloon, it's their "penis." When the body doesn't send enough blood to the penis, it doesn't get as big and strong as it's supposed to, and that's called "Erectile Dysfunction" or "ED" for short.
Now, why does this happen? Well, there's a lot of different reasons. Sometimes it happens because of things that you eat or drink, like too much sugar or alcohol. Sometimes it's because you're sad or stressed out. And sometimes, it's because there's something wrong with your body, like your heart or your blood vessels.
The good news is, there's lots of things that doctors and grown-ups can do to help with ED. They might give you different kinds of medicine or talk with you about ways to be healthier. And really, it's nothing to be embarrassed or ashamed about, because it happens to lots of grown-ups, and there's nothing wrong with getting help when you need it.