I just got back from Hamilton on Tuesday, was up there for a week.
Firstly get your airfares on Jetstar - cheapest by a mile. Check the seasons though as no deals during schools hols. we got 69 pp one way from SYD so 690 all up for my family of 5.
today Jetstar has 2 for 1's I think its 159 one way for 2 pax.
go to Hamilton island homes and check out homes there. homes all include a buggy.
all the hotels based around the main resort do not. u want a buggy.
the kids stay and eat free is main thing.
half a dozen restaurants give kids free meals, eat at those (but u only get these if you book through Hamilton island website or stay in the main resort.
http://www.hihh.com.au/
Best paces to eat are Coca Chu, Reef Terrace Restaurant around the pool of the Reef Towers and Sails in the main resort pool area. You will pay $60 or $70 and the kids are foc. The Animal Park thing is ok - food is average but does a Friday night and Saturday night buffet (average bbq food for $35 per adult - kids foc) and followed by a night tour of the zoo for the nocturnal animals - well worth it)
not sure how old your kids are but if u book any tours - do not take the kids into the office when u book them.
kids are foc if they are 3 or under. last year this was 4 and under. massive diff for the prices charged.
if your kids are even close to 5 or under - just say they are 3. when u get to your tour - no one cares and just takes your ticket.
I have a 7 / 5 and 4 year old. I said I had a 7 and 2 x 3 year olds. save me almost $200.
you have to go to Whitehaven beach - I did the full day tour to Whitehaven and Daydream as reasonable value and great day out on the water.
Daydream is abit old but worth hanging at for half a day. see the wallabies running around and the pools are great for the kids. the tours includes a meal there.
Before you get to Hamilton - do a Coles online shop and it will deliver to your door (probably best for the day after you arrive.) this will save you a fortune as the general store is a complete rip off.
Alcohol cannot be ordered online so take spirits with you - basic beers only on the island - 6 packs are around $23.00 (standard stuff though)
Best Hamilton Island Homes to stay at - Shorelines. If you have 3 or more kids - it wont suit it only has 2 bedders and one will be on the couch.
We stayed at Oasis - high up on the hill but was had an ant problem. I would not recommend it.
Main resort looks ok but remember does not include a buggy. u want a buggy.
it is also quite expensive. all water sports are free if you stay in Hamilton Island Home as well.
I hope this helps a bit. Worth going to - maximum 5 nights.
Best of luck.