I wanted to make matching (mommy and me) dresses and post a tutorial for you, but having no models I had to look up the instructions online. I made a size 4 girls jumper on the fly (it's just a tube of fabric, gathered at the top and trimmed)...
...but had no idea what size to make the doll dress. Soooooo Here is an awesome FREE DOWNLOADABLE PATTERN from "Oliver+S". (I must give credit where credit is due, yes?)
Sorry if this seems a little like cheating....not posting my own tutorial and all... but I just wouldn't feel right taking credit when I would have to use someone else's pattern.
I love that jumpers can be worn as sundresses as well as over shirts and leggings in cooler weather. Enjoy, all!