The birthday girl's favorite colors are aqua (turquoise) and purple. I fell in love with this purple and silver striped fabric when I was shopping for materials. It's very lightweight, so even on the hottest of summer days (and boy we've had some hot ones here this summer) it's still wearable.
I got the pattern for this over at Prudent Baby (one of my new favorite sites for kid projects). They used faux fur for the collar, but I opted to use a sweatshirt material (because I had it in my fabric stash and I feel like it's easier to clean than faux fur).
I used a simple lilac ribbon for the tie on the cape. In the inset photo you can see how the drape a little better (sorry, all I had to model was my iron).
It was really easy to sew up and it turned out fantastic. I know that when I was two, I would have loved running around the yard with this waving in the breeze.