Another choice: what vocabulary words do they want to learn. I ask that question after young students take a field trip to the zoo or a farm. They practice asking the question, "¿Cómo se dice ...?. I teach the word, then allow the student to choose the image we use in an online slide show they can use to show their families, or to review. I have used Haiku Deck and Sway. Both offer good images and their learning curve is not too complex.
Here is an example of a first grade class's choices for animal vocabulary.