The Orchid Mauna Lani is my favorite hotel. They may not have a lot of kids-focused stuff like Westin Maui has, but apparently the property has the quality - used to be Ritz Carlton until a couple of years ago.
They still have swimming pools and some beach activities going on all the time, so kids should be fine.
I stayed there a couple of times and I always like the experience. This year, I stayed using free weekend deal - was upgraded to Executive Ocean Suite. I kind of felt sorry (nah!) not paying a penny for the room!!!
They have a lot of beach stuff including free snokeling equipment (by the way, you are kind of guaranteed to see sea turtles), canoe, walking tours, etc. Oceanside hammock is my favorite - I can just enjoy taking a nap... Not to mention, they have full resort hotel things like spa, tennis courts (w/lessons), golf, etc...
Enjoy your stay!