Thanks, everyone. It helped a lot to read other peoples reasonings and opinions.
It seems to me it will have to be a fictional story based on the actual event. To make it a little easier to understand my dilemma, the event is the voyage of the Mayflower and the story of a child placed with William Brewster. I could use a fictional member of the crew to tell the story of the voyage, but the life of this child before the voyage is pivotal to the story. It seems I have to make the whole story fictional ( which doesn't set well with my love of history) or forget about writing this story. I have made similar changes and noted them in my author's notes before, but never in a situation like this.