One thing parents have asked me about in telling stories to their children is the interrupting. It can be disconcerting when you are in the flow of a story and you hear a little voice going off on a tangent. When my 8 year old interrupts, I incorporate whatever she says and then take it from there. It might completely change the story I was telling, but the nature of storytelling is the interaction between storyteller and listener/s and by accepting her changes, the story becomes more meaningful for her. I can see from her face and her reactions how much more she gets into the story when I incorporate her changes.
However, when my 4 year old interrupts, I am not always sure what she is saying. So I cling onto any subject and verb I hear from her and try to incorporate that into the story. Sometimes I get it right, and sometimes not so much. So I try again. At some point I do say, “Ok, lets go on with the story” and she usually accepts that and we continue.
Sometimes they want a joint story, but my 8 year old gets frustrated with my 4 year olds interruptions, so I try to stick to telling them separate stories. I tell parents when your children are so far apart in age as mine are, they might have to tell separate stories just because of the gap in their intellectual and emotional development.