Hawaii is an easy destination with children in most ways and one hard one: it is a long flight, and the time difference lands badly for young children. Everything else about it is unusually forgiving.
Which island
Oahu is the easiest first choice. The most infrastructure, the widest range of accommodation, calm beaches on the south and west shores, and enough to do that a rainy morning is not a crisis. It is also the busiest.
Maui balances beaches and scenery well, with gentle swimming on the west and south coasts. The road to Hana is spectacular and a genuinely bad idea with young children — it is hours of switchbacks.
Kauai is the most beautiful and the least convenient. Fewer facilities, more driving, and the best parts need effort. Better with older children.
The Big Island has the most variety, including volcanic landscape that children find genuinely astonishing, but distances are long and you will spend real time in the car.
With young children, pick one island. Island-hopping burns days in airports.
Getting the timing right
Stay a minimum of a week, ideally longer. The flight is too long to justify less.
Expect the first two days to be a write-off while everyone adjusts. Plan nothing, stay near the accommodation, and let the schedule settle. Trying to sightsee through jet lag is how the trip starts badly.
What to build the days around
Water, mostly. Calm, shallow beaches occupy children for entire days at no cost and with no planning. Ask locally which beaches are safe for the season — surf varies enormously by coast and month, and a beach that is calm in summer can be dangerous in winter.
Early starts. Everyone is awake at five anyway for the first few days. Use it: beaches and trails are empty and cool.
One outing a day, in the morning. Afternoons at the accommodation.
Practical
Sun protection beyond what feels necessary. Rash vests are better than repeated cream on children, and reef-safe sunscreen is required in places.
Book accommodation with a kitchen. Eating out three times a day with children in Hawaii is both expensive and tiring.
And hire the car seat in advance rather than assuming availability.
