Local clubs work really well. Ours has 50+ members. We have the organisation, cash and drive to have learn to sail classes and a Junior class that gets kids out there on their own gear (mostly) or club owned gear.
Critical mass is vital, and since our kid's programme is only a couple of years old it's still building up. The kids (8 to 15) love meeting kids from the other organised fleets in our neighbouring cities. They do a few short races, then the younger kids spend a few hours sailing around three to a board, then taking the rigs off and splash around, then in the evenings they play Magic.
Those who don't have kids and whose ideas about kids today is driven by media may think that they are all crazed adrenalin junkies, but what they really seem to love is a mixture of structure, free time to mess around and be kids with other kids, and simply being social.
The other thing that organised clubs can do is address the gap between experienced windsurfers and the newbies, which is so big that is's a problem for our sport. Oh, and they can do publicity, a place to store gear, safety, etc etc etc.