Padraig,
you have described a detailed Engage set of activities for children around the theme of the solar system. Children should be encouraged to share what they know and to pose simple questions around what they would like to know more about.
The formation of the solar system is an area of science that still has lots of research going on. What I find interesting is that astronomy is such an observational science -we have to look and see, then try to work out why it is the way we see it, then make predictions that fit within that theory and then go looking for evidence of that prediction.
Here are 18 unanswered questions about the solar system.