nth-child not working after first

Hey all, I have a small problem where I am trying to move a collection of images across a background (they are all the same image but I want to target them individually so I have pasted multiple links as can be seen below, if there's a better way around this feel free to explain) the problem is I can target the first img in CSS with either first-child or nth-child but the following children seem unmoved by the exact same CSS

The three img are all children of .background as far as I'm aware?

<div class="container clearfix">
        <div class="background">
            <img src=../GraphicArt/InkScape/g4109.png alt="1">
            <img src=../GraphicArt/InkScape/g4109.png alt="2">
            <img src=../GraphicArt/InkScape/g4109.png alt="3">
        </div>  
        <div class="head"></div>
        <div class="Rhead"></div>   

I can target the first child but the others are not even targeted

div.background img:nth-child(1) {
    left:540px;
    top:160px;
    position:relative;
};

div.background img:nth-child(2) {
    left:200px;
    top:156px;
    position:relative;
};

Here is the CSS for .background

.background {
    height:600px;
    width:1000px;
    background: salmon url('../../GraphicArt/Inkscape/g4106.png' ) ;
    background-repeat: no-repeat;
    position:relative;
}

Thanks in advance :)