Pamela,
I recommend explicitly setting out the inquiry steps for children, and ask them to engage, (with a prompt, wondering and exploring) and then set up a starter questions that they make a prediction based on their own understanding.
If they are doing research from books, then they will have to refine their starter question and use the knowledge to verify their own mental models – this is different from doing research to find out facts.
So, in response to
What are the differences between the planets?
children might wonder: does the distance from the Sun affect the temperature of a planet? and predict that closer to the Sun will be hotter, and can then check that.
The next step could be finding out why the 2nd planet from the Sun is hotter than the closest planet to the Sun.