I think the kids would love NBA City. It is an NBA themed restaurant with a game area which features pop shot type games as well as video basketball games. My son likes to play there and my husband and I enjoy a bit of "alone time" at our table (though I must say, we enjoy a game of pop a shot as much as the next guy!). The photos also come out great! Each table at the restaurant has a view of a TV that plays highlight films, player interviews and I'm sure, basketball games in season. Kids seem to also like the NBA player handprints on basketball sized models all around the outside of the place.
My 11 year old son is here with me and I just asked him what his favorite thing to do is at Universal when not at the parks and he said "go to the pool" He refers to the HRH pool and if you are there and weather permits you may want to check it out.
There is also a large movie multiplex on Citywalk if the evenings get a bit dull. We have not been to this theater yet as we always find other ways to amuse ourselves.
We have not yet ventured to this off site attraction, but the Pirate Dinner Adventure gets pretty good reviews among those with kids. From what I hear, it is only 5-10 minutes away from Universal.
For us, I have found that overplanning activities backfires and that kids are subject to overstimulation and often their choice is a simpler pleasure such as my son wishing to play by the pool.
I hope you have a great trip!