I really like Rustic Fruit Desserts by Cory Schreiber and Julie Richardson.The subtitle is Crumbles, Buckles, Cobblers, Pandowdies, and More, to give the picture. Easy to put together desserts with lots of flavor. I think a nine year old could handle most of the recipes in it pretty readily, and these kinds of recipes are pretty forgiving, so someone who is learning shouldn't have discouraging failures. The desserts cover all the seasons, so it's not just for the peak of summer, and there's plenty of scope for substituting other fruits thsn those called for in the recipe title. It's a small book, a good size for a child to handle. Judging by the EYB notes on this book, I'm not alone in in finding it a mainstay.
Fika is also good; the blackberry almond cake is my favorite in the book.