The recently renovated Sheraton Waikiki has a lovely pool overlooking Waikiki beach, and a special kids splash area. There's also a drop-in day care, and in-hotel shopping. The Sheraton's farm-to-table buffet offers free or reduced price meals for children, depending on age. There's also poolside dining and even a hot dog shack.
If you need childcare for a very young child, it's worth mentioning that the Sheraton Waikiki has the only program I've found that accepts very young children (ages 3 months old and up). Children 2.5 years and under are limited to 5 hours of care during a one-week period.