On of most important aspects of any class setting is creating supportive environment where people feel safe to express ideas. "It takes courage to be creative" I always say to my students. And I explain that by being vulnerable we grow as individuals and display courage.
Pre-teens are especially conscious of their peers and teachers. It is important to emphasize that their ideas matter. That they can make mistakes, they can decide if they don't like direction, it is okay to change it.
As an educator I do my best to support ideas and to encourage students to come up with ideas. Also to respect other students ideas.
To emphasize ideation as well as respect, I use brainstorming. Students write down their ideas on stickies put them on the wall and discuss as a group about different directions for their work.
Students are free to use their initial idea for the theme of the project or get inspiration for a different idea from the wall of stickies.