Personally, I think they will be bored out of their minds unless they go to shows a lot. i saw the show and enjoyed it quite a bit, but found myself getting restless when the stage business wasn't keeping my interest. The score is hard for an adult to appreciate on first listening; I can't imagine that not being more true for kids. Really, do yourself and them a favor and take them to any number of shows for which you can get tickets (depending on how soon you re going), many on TKTS the day of the performance. Don't know what you / they have seen, but any of these would be more fun for them: School of Rock, Anastasia, Wicked, Kinky Boots (don't rule it out if you / they have not seen it -- this is a PG-13 very warm musical whose story is simple, whose humor is obvious, etc.), Phantom, Hello Dolly if Donna Murphy is performing, Aladdin, Lion King, Beautiful (simple story, a lot of songs that they have probably heard even if they are not aware of them), even Miss Saigon, although you should know that there are a couple of numbers that are pretty lurid. Everyone of them is a better choice for kids 10 - 13.
Stay away from Charlie and the Chocolate Factory...I know no-one who liked it at all (have to admit that I have not seen it). And. Cats. Stinks..