How to make flex child height to wrap content

What I basically want is to make each child element's height to wrap its content.

Here is my code:

<style>

.parent{
        display: flex;
    }

.child{

    padding: 5px;
    margin: 10px;
    background: green;
    height: auto;
}   

</style>

<div class="parent">

    <div class="child">child1</div>
    <div class="child">child2</div>
    <div class="child">child3</div>
    <div class="child" style="height:50px">child1</div>

</div>

Output:

Expected output: