$.ajax({
        url: "createchild.php",
        type: 'POST',
        data: ({ATU:ATUv,AM:AMv,ATS:ATSv,segment:segmentv,acrcat:acrcatv,owner:childowner,topparent:childtp}),
        success: function(msg) {
            console.log(msg);
    }

<?php
header('Content-type: text/plain; charset=utf-8');
$servername = "xxxxxxxxxxxxx";
$username = "xxxxxxxxxxxxxxxxxxxx";
$password = "xxxxxxxxxxxxxxx";
$dbname = "xxxxxxxxxxxxx";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
$sql ="INSERT INTO tablename (top_parent, qualified,retry,partner_attached,partner_name,migration,sap,AM,ATS,ATU,owner,engagement,segment,acr_cat,childtp)
VALUES ('" . $_POST['childname'] . "','No','Unknown','No','Unknown','Not Qualified','Not Qualified','" . $_POST['AM'] . "','" . $_POST['ATS'] . "','" . $_POST['ATU'] . "','" . $_POST['owner'] . "','No','" . $_POST['segment'] . "','" . $_POST['acrcat'] . "','" . $_POST['topparent'] . "'); ";

if ($conn->multi_query($sql) === TRUE) {
    echo "New record created successfully";
    echo "".$_POST['$childname']."";

} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
    echo "".$_POST['$childname']."";
}

$conn->close();
?>