What a darling little sweater that is! I'm not sure I'd add anything to it myself, but if you are looking for some ways to add crocheting to the edges of a knit item, I have a few videos and articles on my website that show how to do just that, only on baby blankets. The concept would be the same though.
If you click HERE, you'll see all my posts on crochet borders. Have fun with it and I hope you find something helpful there. If not, just holler!