I took my son (then, 18 months old) to this during EMH in March 2008 -- he absolutely loved it, then (I can only imagine his reaction when we return in September!).
For those not in the know, it's basically a dance party with music and lights in the Playhouse Disney Theatre at DHS (it was only running during EMH) which caters to small kids. It's a lot of fun, if you enjoy loud music and dance-floor style lighting.
As for the characters, all the "traditional" Disney characters were present (no Handy Manny, Little Einsteins, etc.). Lots of interaction can be found, here.