Turtle beach is actually another name for Laniakea Beach.... its just south of the North Shore town of Haleiwa down the King Kamehameha Highway.
Here is a website with details:
http://www.portaloha.com/SecretsOfHawaii/Laniakea.htm
You might also take a look at the other things on that website I posted above for ideas on what might appeal to your family as far as touring.
Last year when I was researching for our trip, I actually put together a thread for folks that were going to Aulani in December. On the first post of that thread, I linked to lots of good websites that I had found about Oahu at Christmas time.
You might find that first page of the thread & its links helpful, here is the link to that:
http://www.disboards.com/showthread.php?t=3117807
Also, if you do Pearl Harbor they have a really cool activity book for the kids to fill out as you all go through the tour, I believe you get them in the giftshop for free, but I think their may be more details on the govt's reservation website. Its geared towards the younger set, so we didnt use it, but I saw many younger kids filling theirs out and really enjoying the process of what otherwise might be lost on them.
Here is the link to the pearl harbor online reservation site:
http://www.recreation.gov/tourParkDetail.do?contractCode=NRSO&parkId=72369
Here is the link to the Pearl Harbor info for kids:
http://www.nps.gov/valr/forkids/index.htm
I would also check out this website on Things to do on Oahu:
http://www.aloha-hawaii.com/oahu/things-to-do/
There is really a lot to do on Oahu and its just a process of elimination as you cant possibly do it all.
I think the kids would really enjoy Turtle Beach (especially if you get there when the turtles are laying out on the beach)... and the Northshore, be sure to get a shave Ice at Matsumotos up there in Haleiwa as well as trying out the yummy shrimp trucks in the area such as Mackys or Giovanni's.
Though with a 1 year old in tow you may decide to divide and conquer on some things that the older kids may enjoy... or just relax at the resort.