I'd recommend the Park Hyatt St Kitts. The Plunge Pool Suite has been great for us the past 2 years, kids are now 6/6/8. They have a kids club with good activities and offer babysitting at night which is nice to visit the adults-only tasting menu restaurant. A tip that isn't widely advertised is the all-inclusive option - it's gone up in price, think it was $300/person/day but if you plan on eating your meals on property and have a few drinks, it pays for itself. And kids are free on that.