We were there xmas, CNY & just easter. My 3 yr old LOVES it there as he is really into swimming. Chaweng is a good start if it's your first visit as everything is within walking distance. Beaches are lovely & there are always other kids to make friends/play with. With our familiarity on the island, we stay at this quiet resort called Am Samui (HKD700 a nite for your own villa!) on Taling Ngam Beach. It's family run and very quaint. Trouble is you have to hire a car to get around the island as there are limited restaurants nearby. Lamai is good too but beaches not the best. There is a playroom called Kids Club in Lamai (like HKD50 per hr!), which we went during the hottest hours from 1-3 pm when our little boy didn't want to nap. If money is not an issue, Four Seasons is GORgeous though you need to get around the ''estate'' in a buggy driven by hotel staff, which makes it difficult to just pop back into your room. I think the best time/weather to go is CNY. Easter gets very hot and our son is seriously lathered in sun cream. Book early though as there's only 1 direct flight a day & is always booked up.