Aida is the story of a love triangel between an Egyptian princess, the Egyptian captain betroved to her, and a Nubian princess who has been captured by the captain. The music in it is fantastic (written by Tim Rice and Elton John). I've seen it a couple of times on Broadway, and a couple of times on tour in Boston.
I'm not sure how much it would hold the interest of 13 and 9 year old boys, though. I don't think I'd take my 13 and 9 year old nephews. There is more dialog in it than in the Lion King or Joseph. Those shows are geared towards families--Aida seems a bit more adult to me.
Are you thinking of going to see it at the North Shore Music Theatre? Their productions are usually very good, but the sets are somewhat limited at times when compared to Broadway or the tours.
Not sure if I helped, but at least I'm giving this a bump. Perhaps someone who has taken kids will see this and respond.
Karen