Targeting first 2 children or last 2 children

For the first two children you can use:

ul li:nth-child(-n + 2) {
    color: orange;
}

http://jsfiddle.net/nYnSz/1/

For the last two:

ul li:nth-last-child(-n + 2) {
    color: orange;
}

http://jsfiddle.net/nYnSz/