David A. Adler
The illustrations are fun and sometime comical. I think that kids who want to know how roman numerals work will easily pick it up after reading this book. I feel it may be a bit long for a read aloud, but it could easily be broken up between a couple of days, or even a week.
I know I was intrigued with Roman numerals at about 9 or 10 and I wish I would have had this book back then : )