Sam,
the joy of the inquiry approach is that you can take children’s ideas and explanations and help them structure them into testable investigations.
If a child sees that an unpeeled orange floats, but when you take the peel off and make it lighter it sinks, they then have to work into their thinking the idea of buoyancy. You might help them think of the peel as being like a life jacket.
We wear life jackets on the water, but they make us heavier! and more floaty!
You don’t need to be the expert on the science, in fact I often recommend being slightly baffled — tell the children that last year the class did something different so you aren’t sure.
When I make paper – straw rocket with a group, many of the children will ask me if they have done it right. My only answer to them is “try it and see.”