Totally Agree with PP. I have eaten at both in the last six months, and found the food quality comparable. I don't have kids, but may take my niece in the next year...I wouldn't think of taking her to Jiko (she's well behaved, but I think she wouldn't like it.) I wold consider taking her to California Grill, but only if we could get reservations around fireworks time. If your kids enjoy that type of dining, it might be worth it any time.
I'd keep Jiko hands down. Jiko and Boma were two of the many reasons we decided to buy in at AKV for the short term (realizing restaurants will morph over the years).
If the 9:20 time is anywhere near the start time for Wishes, I think you should keep the CG reservation. We have dined at both, and enjoyed both. However, we much prefer CG especially if it is fireworks time at the MK!