First-child pseudo-class in css 2.1

First-child pseudo-class in css 2.1

I don't know where to put pseudo class in this definition:
#recently_played_grid li img {
margin-left: 10px;
}
I want to set margin-left to 0px just in a first child of the list. Should
I do
#recently_played_grid li:first-child img
?
It doesn't seem to work