As Mike said you should be able to easily make it to the Cays and and back, maybe even Bequia, in 7 days.
Petit St. Vincent may have changed since you visited, now yacht crew are only allowed to go to the beach bar, Goaties, not the one on the hill anymore and the small beach next to it. It's a nice stop for a lunchtime drink and a swim but it might be boring for the kids. We usually stop for a drink then dingy over to Petit Martinque for a hike around the island.
Myopian (sp) is near there and maybe someone will have more information on that.

Drink all day at home, your friends worry about you; do it on vacation and they say "what a good time you're having". Save your friends needless worry, travel more!