Modifying kids' t-shirts? Sewing Machines Parts and Sales in Los Angeles

A local kids clothing store is selling plain t-shirts at $1.99, which is insane for here. So I bought a few, thinking they'd make good practice material for experimenting with…alterations? I'm not sure that's the right word, when I'm really just talking about decals, ribbons, and pockets.

Anyway, I got some and now I'm looking around for ideas on what I could do, and finding…there aren't many. Everything seems to be for making women's shirts sexier. The only thing I currently have planned is to try and appliqué a shark onto one, since my daughter asked if I could make her "a shark shirt, but a girl shirt, just with a shark on it." I've never done appliqué, but it seems straightforward, and my husband has the art skills to produce a recognizable shark silhouette (I don't). But what to do with the others? What embellishments or changes would you make to a kid's long-sleeved shirt? (These ones are all girl colours. They were out of the boy ones)