This weekend South Street Seaport's Spiegeltent was taken over by the king of gruppy kids' music, Dan Zanes, and his band of merry men and women. Parents rocked out, kids danced their fool heads off, and sea chanteys were sung by the score. New York was there to talk to the endlessly cheerful Zanes — who before he was your toddler's hero was a member of eighties college-rock faves the Del Fuegos — and to catch the show.