First, you should use Bootstrap 4.0 or above to get flex support.
Second, try this:
<style>
.parent { background: blue; }
.child {
background: grey;
height: 50px;
}
</style>
<div class="parent d-flex flex-wrap" >
<div class="child m-1">item1</div>
<div class="child m-1">item2</div>
<div class="child m-1">item3</div>
<div class="child m-1">item4</div>
</div>
<br/>
<div class="parent d-flex justify-content-start" >
<div class="child m-1">item1</div>
<div class="child m-1">item2</div>
<div class="child m-1">item3</div>
<div class="child m-1">item4</div>
</div>
<br/>
<div class="parent d-flex justify-content-end" >
<div class="child m-1">item1</div>
<div class="child m-1">item2</div>
<div class="child m-1">item3</div>
<div class="child m-1">item4</div>
</div>
<br/>
<div class="parent d-flex justify-content-center" >
<div class="child m-1">item1</div>
<div class="child m-1">item2</div>
<div class="child m-1">item3</div>
<div class="child m-1">item4</div>
</div>
<br/>
<div class="parent d-flex justify-content-between" >
<div class="child m-1">item1</div>
<div class="child m-1">item2</div>
<div class="child m-1">item3</div>
<div class="child m-1">item4</div>
</div>