So I went back pack shopping for my 3 yr old and I thought it was going to be this fun and easy thing. Now I'm so confused. I had no idea there were different sizes. Do I get her a regular size 16" for preschool or a mini 13"?? The regular size looks so big but will fit her lunchbox, change of clothes, and projects. I'm not sure the 13" will even though it looks a lot better on her. Here's a pic of the regular size, what do you guys think?