[wvxvw]

Про порядок никто не говорил

private function test():void 
{
    var list:XMLList = 
    <>
        <foo attribute="0"/>
        <foo attribute="1"/>
        <foo attribute="2"/>
        <foo attribute="3"/>
        <foo attribute="4"/>
        <foo attribute="5"/>
        <foo attribute="6"/>
        <foo attribute="7"/>
        <foo attribute="8"/>
        <foo attribute="9"/>
    </>;
    var child:int;
    var result:XMLList = new XMLList();
    while (result.length() < 5)
    {
        child = Math.random() * list.length();
        result += list[child];
        delete list[child];
    }
    trace(result);
}