To be honest, there are a whole lot of sunglasses that are suitable for your younger sister. Whenever you visit a big e-commerce website, you are able to see millions of cute sunglasses of different types. Here I recommend moustache sunglasses for her because that kind of sunglasses is really amazing and funny. Just browse through the Internet, Ebay and Alibaba have got a great deal in stock.
If you want to buy the cute sunglasses for your younger sister, you could take the ray-ban junior sunglasses into consideration. You'd better go to the amazon to have a search because the price there is suitable and the quality is good. Then you can choose the one with suitable color and the material.