I followed the pattern for a size 4, but my daughter is only 3 and she is considered pretty big for her age so I think this is going to be a bit big on my niece for a while who is smaller and younger. That's alright though because then she can wear it longer.
I had actually started sewing the zipper in with the sewing machine and it looked fine on the sweater, for some reason my bobbin wouldn't wind correctly though so it would keep getting jammed up. I am just a really slow hand sewer so I prefer to use the machine when I can. I found a really good blog online that helped me do the zipper, it is http://acunningplan.typepad.com/andsheknitstoo/2005/09/zippers_101.html
I didn't follow it to the T but it helped me tremendously and has great pictures.
Thanks jamadian75 for redoing the link for me, I didn't even think about the comma! :doh: