If we are talking about 5,6 and 7 year olds,it would have to be someone that they knew,ie a pop star or TV personality. Or local person/business as Christopher suggests.
Their interest would soon wane otherwise,if an historical figure was chosen.
Not real There are a great many people who have listened to "The Archers" for so many years that they regard them as a part of the family.
A historical character would put many off immediately ... a variation on dates and Henry VIII and his six wives ... pop stars or footballers might be the best idea. I'm reading about Lulu at the moment.