We've stayed both at the Hilton and the Mauna Lani with our two kids over the years. When they were younger, the Hilton was the place to be for its choice of pools with slides, and the boats, dolphins, lagoon, etc. also were fun for them. The rooms were nice enough, but not luxurious. The luau and the restaurants ok, too. They had a nice little gift pack for the kids when we checked in-- and those things go a long with kids!
Our last stay was at the Mauna Lani. Now that the kids are teens, it was a better choice for us. The rooms are nicer than I remember the Hilton's being, and the clientele in general is older than at the Hilton (i.e. less little kids). I don't remember any problem with the swimming pool at all. We like to snorkel, so enjoyed their little snorkel cove, which is just a short walk from the hotel proper. Also, they have a nice swimming beach with cabanas and surf/boogie gear to rent. We haven't stayed at the Orchid, but did go there for brunch one day and looked around. It looks even more luxurious than the Mauna Lani, maybe too much so for little kids. All things considered, I might take advantage of the rates at the Mauna Lani.