select first child with jquery

Programmer Question

I am trying to select first child of ul and then remove it and then append it in the end of that ul but unfortunately i can not selet first child.

Here is code

current = 0;
$(document).ready(function(){

    width=951;

    var totalSlides=$(".slider ul li").length;
    $(".slider ul").removeAttr('width');
    $(".slider ul").attr('width',width*totalSlides);

    $('#next img').click(function(){
        current -= width;
        $(".slider ul").animate({"left":current+"px"}, "slow");
        $(".slider ul").append($(".slider ul:first-child"));
        //$('.slider ul:firstChild').remove();
    });
});

Find the answer here