Decide by what her stepson likes to do...does he have a favorite character? If he isn't into that...maybe a recreational activity would be cooler than dinner for him...like letting him rent one of the little boats for an hour, surfing at typhoon lagoon, horseback riding. Something that he would like to try, but doesn't have the opportunity to do at home.
My daughter wanted dinner with the pooh characters...it was great. They sang to her (actually the whole restaurant), brought her a lit cupcake. It was excellent.