I was talking to a friend who was remarking that at her brothers 13th birthday they did everything in 13's. There was 13 kids, the party was on the 13th, etc. They also watched Friday the 13th movies, but I don't approve of that kind of thing for ADULTS! let alone kids. But that's one of those things that depends on the parent.
I don't know if DS means that your child is a girl or boy, but when I turned 13 my mom had a friend of hers (who was a makeup artist) out to teach me and a few friends how to put on makeup. That was cool. Kinda a getting to be a grown up type thing.
Anyway, good luck, and congratulations.