My wife and I had been to Oahu and Maui a few times. We chose to take our kids first to Oahu so they could see the things there that needed to be seen. The Arizona Memorial, Temple and to some degree the PCC (not high on my list). We also spent some time on Waikiki, Hanauma Bay and the Dole factory.

Then, after that was all handled, we took them to Maui and got away from all the nastiness of Oahu so they could enjoy and appreciate more of what Hawaii really is. Even Maui is becoming more and more Waikiki-ish, but given the choice between the two Maui is a no brainer.