HI, I mean HI isn't as expensive as people may think.
As generic as it may sound, it really depends on what you want to do. Aulani has a lot to do without spending too much money like the spectacular pool and also the kids club which is modeled after DCL if you ever cruised.
Honestly for a 2 week period including food, activities and car: $3,000 will give you a good time. If you are drinkers add another $500.
Keep in mind that you will not always be eating on property or out all the time. Save some money by cooking at least 1 or 2 meals a day and breakfast being the easiest to prepare. There are many places to eat within 5 miles or across the street that will not break your bank.
As far as attractions it depends on how extravagant you want to get but looking at the age of your little ones that may save you money on doing the crazy stuff like para sailing.
I would recommend the Polynesian Cultural Center which is an all day event/village. The cost I think ranges from $40-60 pp I think. Attractions like the Arizona Memorial and Waikiki beach are free. Hanama Bay where you can snorkel is very nominal in terms of fees.
What really breaks you, like any vacation, is the the cost of buying souvenirs! Trust me the store in Aulani will break you! Sounds like you are very excited. If you have any specific questions please feel free to ask.