Edit in JSFiddle

/* Formatting function for row details - modify as you need */
function format ( d ) {
    // `d` is the original data object for the row
    return '<table cellpadding="5" cellspacing="0" border="0" style="padding-left:50px;">'+
        '<tr>'+
            '<td>Full name:</td>'+
            '<td>'+d.name+'</td>'+
        '</tr>'+
        '<tr>'+
            '<td>Extension number:</td>'+
            '<td>'+d.extn+'</td>'+
        '</tr>'+
        '<tr>'+
            '<td>Extra info:</td>'+
            '<td>And any further details here (images etc)...</td>'+
        '</tr>'+
    '</table>';
}

$(document).ready(function() {
    var table = $('#example').DataTable({
        'ajax': 'https://api.myjson.com/bins/16lp6',
        'columns': [
            {
                'className':      'details-control',
                'orderable':      false,
                'data':           null,
                'defaultContent': ''
            },
            { 'data': 'name' },
            { 'data': 'position' },
            { 'data': 'office' },
            { 'data': 'salary' }
        ],
        'order': [[1, 'asc']]
    } );

    // Add event listener for opening and closing details
    $('#example tbody').on('click', 'td.details-control', function(){
        var tr = $(this).closest('tr');
        var row = table.row( tr );

        if(row.child.isShown()){
            // This row is already open - close it
            row.child.hide();
            tr.removeClass('shown');
        } else {
            // Open this row
            row.child(format(row.data())).show();
            tr.addClass('shown');
        }
    });

    // Handle click on "Expand All" button
    $('#btn-show-all-children').on('click', function(){
        // Enumerate all rows
        table.rows().every(function(){
            // If row has details collapsed
            if(!this.child.isShown()){
                // Open this row
                this.child(format(this.data())).show();
                $(this.node()).addClass('shown');
            }
        });
    });

    // Handle click on "Collapse All" button
    $('#btn-hide-all-children').on('click', function(){
        // Enumerate all rows
        table.rows().every(function(){
            // If row has details expanded
            if(this.child.isShown()){
                // Collapse row details
                this.child.hide();
                $(this.node()).removeClass('shown');
            }
        });
    });
});
<h3><a target="_blank" href="https://www.gyrocode.com/articles/jquery-datatables-how-to-expand-collapse-all-child-rows/">jQuery DataTables: How to expand/collapse all child rows</a> <small>Regular table</small></h3>

<button id="btn-show-all-children" type="button">Expand All</button>
<button id="btn-hide-all-children" type="button">Collapse All</button>
<hr>
<table id="example" class="display" cellspacing="0" width="100%">
    <thead>
        <tr>
				    <th></th>
            <th>Name</th>
            <th>Position</th>
            <th>Office</th>
            <th>Salary</th>
        </tr>
    </thead>
    <tfoot>
        <tr>
				    <th></th>
            <th>Name</th>
            <th>Position</th>
            <th>Office</th>
            <th>Salary</th>
        </tr>
    </tfoot>
</table>
td.details-control {
    background: url('https://cdn.rawgit.com/DataTables/DataTables/6c7ada53ebc228ea9bc28b1b216e793b1825d188/examples/resources/details_open.png') no-repeat center center;
    cursor: pointer;
}
tr.shown td.details-control {
    background: url('https://cdn.rawgit.com/DataTables/DataTables/6c7ada53ebc228ea9bc28b1b216e793b1825d188/examples/resources/details_close.png') no-repeat center center;
}

External resources loaded into this fiddle: