My daughter (now middle-aged, though she will probably hate my writing that) was diagnosed with celiac disease when a toddler. Back then, it was very difficult to find recipes for treats without gluten. I made and decorated a sheet "cake" that was really chocolate fudge, and she enjoyed it for her birthday. She practically lived on bananas and rice for a while (there weren't even rice cakes when she was small).
However, today you can find even gluten-free cake mixes, as well as a mix for cookies and one for brownies in the supermarket by a mainstream company, Betty Crocker. There are additional recipes on www.bettycrocker.com that will allow the home baker to adapt their mixes to make various types of treats.
If you like to bake and are even fairly good at it, two cookbooks you may want to try are: THE GLUTEN-FREE GOURMET (Living Well Without Wheat) by Bette Hagman, and HEALING FOODS (Cooking for Celiacs, Colitis, Crohn's and IBS, by Sandra Ramacher. The latter has recipes that are totally grain-free, gluten-free, sugar-free and lactose-free.
In addition, there are online bakeries specializing in gluten-free products and others for special diets. You can find them via a search engine, and they will ship already baked treats, such as gluten-free cakes, to you. Some even pack frozen foods using dry ice. Mariposa.com is one artisan bakery that sells gluten-free products online. Good luck! JAYE