There are so many great options out there! Why not consider looking away from the children's section in your local department store. Many "adult" designs are available in single and king single sizes, or take a look online for amazing Australian designers who have a unique aesthetic. Here is a handful of great kid's linen that is anything but expected.
1a. Castle // Blue Velvet Quilt Cover
1b. Castle // Watermelon Penny Round Cushion
2. Incy Interiors // Croc Pastel Quilt and Pillowcase set
3. The Print Society // Sunny Days Pom Pom Cushion
4. Kate Lauren // Zachary Hunter Sheet Set
5. Ikea // Odestrad Quilt Cover and Pillowcase set
6. West Elm // Shibori Cushion Cover