You can definitely use essaypop for the younger kids. Many of the pre-made lessons in the lesson library are currently aimed at middle school students, but most of them can be adapted to elementary grades. Go to the middle school lessons and see how you might adapt them for your students, as they all can be easily modified to fit you and your students' needs
You can also create your own lessons by going to the "create" tab and selecting the purple "assignments" tile. This will take you to our wizard where you can build your own lessons. Follow the prompts and build your lesson plan, and when your done, it will be stored under the "library" tab in the "my prompts" area. I would choose from the "pop question" or "short response" templates for elementary students.