One of the perhaps ironic things about creating a lesson plan that cultivates curiosity for kids, is that you do have to provide some structure. Giving kids a specific framework from which to create their own concepts within makes it easier than giving carte blanche saying “write something unique… make something up etc.”
For example, in my grades 3-6 lesson plan “what’s their story”, as a pre-cursor to story writing, all I ask the child to do in the lesson is to create characters, but I give them an illustration first, from which they can let their mind run free.
Another aspect of evoking creativity, is to know when to make it as non-competitive an environment as possible. Some students take more naturally to being creative than others, so it is that it can stifle a child’s attempt when they are comparing themselves with another student with a knack for it.
Lastly, loosen students and yourself up before hand. Either in context, or within the lesson plan itself. Creatovity is the domain of avoiding self-restraint. The same way adults whom are creative have messier offices than those who aren’t, perhaps prime the students before hand with as many seemingly non-releated things as you can. Creative is an inter-disciplanry art. Even something like having a list of words or images atop a lesson plan can sway a student to move forward in that direction. All creativity has to emanate from somewhere after all.