Just wanted to clarify--Whispering Canyon isn't at the MK...the way your post is worded it seems to imply that you think it is.
California Grill is an upscale "fine dining " experience. It's not really a meat and potatos place, so I think a lot depends on two things. First, will you enjoy the cuisine? Next, are your kids used to eating in a fine dining experience, or is the extent of their eating out experience Bennigans and Chucky Cheese? If the latter is the case, then IMHO trying fine dining after a long day in the parks is not appropriate. It's not fair to your kids or other patrons. Many kids simply can't handle sitting still and talking quietly for an average two hour meal after a full day.
If you are thinking about eating there for the fireworks, at 16 days out you are probably too late to get a reservation at that time. And in all honesty, the fireworks are much better from inside the MK. There's no guarantee of getting a fireworks view table either.
And as an FYI, there is a requested dress code of business casual for the CG--it sounds like you plan on being "Park Commando's" so this might not work for you.
Anne