I just answered DC's questions as they asked.
I do remember a tragic occasion when DC were about 6 and 8 when a boy DS used to play with at school was killed in a road accident. It was Library day, so that is where we went after school and DC picked out the MacDonald Book of the body.
When we got home, I didn't even get time to take my coat off before DS, in particular was asking me to read the book with him. so i just sat on the floor, a child both sides and we covered everything, reprised the basic facts that both knew, covered menstruation and periods and then discussed death, what it meant, what might happen.
Then DS got up and put the tv on, which I recognised as him having learned as much as he wanted and he would now go away and think about it and come back with questions a couple of weeks later.
I remember this event so clearly because DH came home from work, just as we were finishing. I explained what had happened and that supper would be late and he simply went straight out again and bought fish and chips.