I found a Dixie Gun Works 'Cub' flintlock in .40 for my grandson last year.
He loves it (and shoots it better than I do). He's 5 and still needs a bit of help loading, but he shoots from a bench with sandbags himself. Next fall he may try it at the Rendevous in Barton, VT.
P.S. He loves the tomahawk and knife also.
Gotta keep the young ones interested.