The best time for family holidays in the Caribbean is during the British winter. Why fly that far and at such expense when there is summer sun to be had so much closer to home?! Bear in mind that summer (June to November) is also the official hurricane season in the region.
The only real reason to take the kids to the Caribbean in the main UK school holidays or summer months is because it’s cheaper, but you need to be confident that your kids will be able to bear the sometimes unpleasant humidity, especially if they are very young. If you do go at this time of year, choose a property where they can escape the most intense heat of the day, whether it’s in an air-conditioned crèche or kids’ club or a waterpark, and be super-vigilant about sunburn (use parasols) and about drinking enough water. Mosquitoes can be an annoyance too (though there’s no malaria), so go armed with repellent.
July and August are the hottest months in the Caribbean, while the peak season is December to February. For this reason, the prime time for a family holiday in the region is March, April or May, when it’s less crowded but the weather is still lovely.