Jquery Div Fixed Position Scroll

function fixDiv() {
    var $cache = $('.child');
    if ($(window).scrollTop() > 100)
        $cache.css({
            'position': 'fixed',
            'top': '10px'
        });
    else
        $cache.css({
            'position': 'relative',
            'top': 'auto'
        });
}
$(window).scroll(fixDiv);
fixDiv();

<div class="child">This div is going to be fixed</div>