hi, check the hard rock in kuta
bali.hardrockhotels.net/ .
i have a 5 year old boy. we stayed there 3 times ( last visit 3 months ago ) and hopefully will be coming back . good hotel, good location. it's got a huge pool with water slides and sand island in the middle. they do some fun activities for kids ( and adults ) at the pool. plus their kids club is good too. just don't take ground floor rooms 'cause they are little bit damp.
been perfect family holidays so far. surfing reefs in kuta from 6 till 9 am. then chill out with my son at the pool whole day while my missus was doing whatever she wanted to do. shops, massages, etc. we love bali