Last time I was there (2 yrs. ago) there were a number of liveaboards in both the main harbor on moorings and at the east end of the island in coral bay/hurricane hole. I understand the Park Service has been tightening things down there so I don't know the current situation. I think Bill Trayfors might know or you could try the www.ssca.org
The other thing to consider with wife/young kids is the hurricane season. You have to be prepared to get off the boat and lose it if you are gonna stay there year round. It is not a LIKELY scenario but big weather does come through there. Insurance is prohibitively expensive for most people if you are gonna be there "in season". Nice island...some black/white friction and crime but not as bad as St. Thomas. Lots of incredible places to sail to on your time off! Good luck.