Hotel Management v1.0 - Reflected XSS

if (isset($_GET["check_in_date"])) {
 $check_in_date = $_GET["check_in_date"];
 $check_out_date = $_GET["check_out_date"];
 $no_children = $_GET["children"];
 $no_adults = $_GET["adults"];
}
...
<div class="form-group">
 <label for="no_adults">Adults</label>
 <input type="number" class="form-control" name="no_adults" id="no_adults" value="<?php if (isset($no_adults)) {
 echo $no_adults;
} ?>">
</div>

if (isset($_GET["check_in_date"])) {
 $check_in_date = $_GET["check_in_date"];
 $check_out_date = $_GET["check_out_date"];
 $no_children = $_GET["children"];
 $no_adults = $_GET["adults"];
}
...
<div class="form-group">
 <span class="form-label">Check In</span>
 <input class="form-control" name="check_in_date" id="check_in_date" type="text" required value="<?php if (isset($check_in_date)) {
echo $check_in_date;
} ?>"/>
</div>

if (isset($_GET["check_in_date"])) {
 $check_in_date = $_GET["check_in_date"];
 $check_out_date = $_GET["check_out_date"];
 $no_children = $_GET["children"];
 $no_adults = $_GET["adults"];
}
...
<div class="form-group">
 <span class="form-label">Check out</span>
 <input class="form-control" name="check_out_date" id="check_out_date" type="text" required value="<?php if (isset($check_out_date)) {
echo $check_out_date;
} ?>"/>
</div>

if (isset($_GET["check_in_date"])) {
 $check_in_date = $_GET["check_in_date"];
 $check_out_date = $_GET["check_out_date"];
 $no_children = $_GET["children"];
 $no_adults = $_GET["adults"];
}
...
<div class="form-group">
 <label for="no_children">Children</label>
 <input type="number" class="form-control" name="no_children" id="no_children" value="<?php if (isset($no_children)) {
 echo $no_children;
} ?>">
</div>