Personally, I'd take them to a show that is familiar (music or plot wise). So I'd suggest:
Lion King
Mary Poppins
Legally Blonde
*Not Little Mermaid-too many mixed reviews
If they really want to hop onto the theatre band wagon:
Wicked
Rent
Just my two cents.
"That's a good point. Next time I pee on a Starbucks couch and throw straws and napkins at a barista, I'll just yell, "YOU DON'T KNOW ME OUTSIDE OF STARBUCKS! YOU DON'T KNOW ME AT ALL!" and that should do it. "-LizzieCurry