Thanks lepaulate - I really appreciate everything about your post.
We try very hard to be careful and reasonable about what we tell the children and how. Our guide has been to only ask the question that they have asked as honestly as is appropriate. And allow them to ask more questions if they need more info, but not to offer it.
The questions about sharing came about because DP had to leave quite early one Saturday morning to do something with K. DD was clearly trying to understand how sharing time works, which is fine. I'd rather she asked and happy that she felt she can and wanted to.
I'm really not one of those parents who want to be their children's 'mate' and tell them all sorts of adult things they don't want to know and haven't asked.
But it's natural for them to have questions and, I think, healthy to try and answer them honestly where possible.
But I really do appreciate your input. Genuinely.