Writing Prompts. There are a million different ideas out there, so this is my take on it.
The idea is to get the students writing, right? So, why not pose general questions that kids ask all the time back at them? Let them come up with their own answers for why the sky is blue. It doesn't matter, or even should be scientifically correct because it's about motivating the students to want to write and think creatively.
This is a sample of a bigger project that it also posted on this site. It gives a descriptive for teachers as well as an example to read to students to give them a general idea of what you're looking for.
Tired of your general, run-of-the-mill writing prompts? Definitely check out this free sample then. Enjoy!