Waikiki doesn't have a lot of great hotel pools as the beach is the main attraction, most are your regular rectangular pool with some loungers. Not anything that a kid would get super excited about.
As far as Waikiki goes, check out the Hilton Hawaiian Village. HHV is the probably the best family hotel in Waikiki. The downside to HHV is its location relative to Waikiki, a bit of walk to get to the heart of Waikiki. However, HHV is more of a resort than anything else you'd find in Waikiki so you wouldn't necessarily need to leave.
Another hotel in Waikiki to consider is Aston Waikiki Beach Hotel. It has a roof top pool. It is not on the beach but directly across the street from the beach. The ocean in front of the hotel has been walled off creating a calm water area. The hotel has a roof top pool but it is fairly standard.
North Shore is more of a vacation rental type of place, Turtle Bay Resort being the only hotel I can think of in the immediate area. I have stayed there and it is awesome but not cheap.
If/when we go back to Oahu we plan to do exactly what you are thinking about, a couple of days in Waikiki or North Shore and then to Ko Olina. I really need to win the lottery so I can travel full time.