woah, far too much I'm afraid!
Print's method is good of course but I remember what it takes to master the pen-tool
Kellie, as you are a complete newbie, I'd suggest you use the magnetic lasso for this work in two easy steps:
Draw a magnetic lasso around the baby, feather it with one or two pixels, then move this selection (you will have to copy it on a new layer) closer to the left boy.
Then disable this layer, go back to the background and select the boys left arm with the magnetic lasso. As this arm will be above the baby you should feather it with a very small amount, otherwise the edge will become too blurry. Now invert the selection, go back to the second layer and click the add new layer mask icon at the bottom of the layer. The selection will be masked automatically.
Now there's just a bit of the babys head left on the background layer but you'll probably want to darken the background anyway to make then stand out a bit. I did this manually so it's not very good but if you do it properly (with some selections and stuff) it does the trick.
Oh and don't crop as silly as I did, both heads should be centered with the same distance to the borders