i try to make a trigger button from a div children with the same class,but my code below seems not working properly, i try to make a looping at first to get the class box then try to get the children from each box, but it seems not working.

```js
var container = document.querySelector(".container");

var box = document.getElementsByClassName("box");

for(var i = 0; i < box.length; i++){
  var x = box[i].children;
  x.addEventListener("click", function(){
    console.log('hello world')
  })
}
```

```css
.container {
  border: 1px solid black;
  padding: 10px;
}
.box {
  width: 100px;
  height: 100px;
  background: red;
}
```

```html
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>
  <div class="container">
    <div class="box">
      <button class="btn">click me</button>
    </div>
    <div class="box">
      <button class="btn">click me</button>
    </div>
    <div class="box">
      <button class="btn">click me</button>
    </div>
    <div class="box">
      <button class="btn">click me</button>
    </div>
  </div>
</body>
</html>
```