Infinate scrolling on tablets while pulling content with a Json

Question

Im using the scrollExtend plugin to call a Json script which will spit out my content. This works fine on desktops and works well however my site is responsive and I will need this functionality to work on tablets and mobile devices aswell.

I have conducted a lot of test and I have narrowed it down to my Json script:

    <?php

    $parent_query = bb_query("SELECT f_children
        FROM t_articles
        WHERE f_id= '85' and (f_removed IS NULL or f_removed ='0')
    ");
    $parent_row = bb_fetch_assoc($parent_query);

    $children = explode(':',$parent_row['f_children']);

     $i= 1;

        $rowsperpage = 6;    
        $totalpages =  count($children);            
        $_SESSION['highlights_current_page']++;         

        if (isset($_SESSION['highlights_current_page']) && is_numeric($_SESSION['highlights_current_page'])) {
           $currentpage = (int) $_SESSION['highlights_current_page'];
        } 

        if ($currentpage > $totalpages) {$currentpage = $totalpages;} 
        if ($currentpage < 1) {$currentpage = 1;} 

        $offset = ($currentpage-1) * $rowsperpage;    

        $x=0; 
        ##take off earlier articles
        while($x < $offset){
            array_shift($children);
            $x++;
        } 

        ##take off later articles
        $children = array_slice($children, 0, $rowsperpage);


echo $_SESSION['highlights_current_page'];    
echo "current:".$currentpage; 
echo "total:".$totalpages; 
echo "offset:".$offset; 


    foreach($children as $child)
    {  

    $child_query = bb_query("
       SELECT *
        FROM t_articles
        WHERE f_id = {$child}
        and (f_removed IS NULL or f_removed ='0') 
        AND f_live ='1' 
     ");

    while ($row = bb_fetch_assoc($child_query)){

    //data for echoing the articles

    }   
    }

    ?>

When it is displayed on desktops and you scroll down it will then echo the next 6 articles and then if you continue the next 6 and so on. but for tablets it will echo the next 6 articles out and then it when you scroll down it will echo the same 6 articles over and over.

Here is my math for the blocks on desktops: First echoed block of articles: $_SESSION['highlights_current_page']:2 current:2 total:20 offset:6

second echoed block of articles: $_SESSION['highlights_current_page']:3 current:3 total:20 offset:12

third echoed block of articles: $_SESSION['highlights_current_page']:4 current:4 total:20 offset:18

$_SESSION['highlights_current_page'] is the number of how many blocks it has echoed. e.g: the first six echoed would be 2 because six articles start off as displayed are classed as 1.

On tablets it will repeat: First: $_SESSION['highlights_current_page']:2 current:2 total:20 offset:6 Second: $_SESSION['highlights_current_page']:2 current:2 total:20 offset:6 Third: $_SESSION['highlights_current_page']:2 current:2 total:20 offset:6

I'm rather new to programming for tablets is there something that I've added that wont work, or can anyone see the issue with my maths?

Thank you in advance