You'll probably find opposing opinions rather than a consensus, so keep that in mind. I would choose California Grill hands-down. We have eaten there 4-6 times and always had a good meal. We enjoy the ambiance, and while it's a signature restaurant, it is also pretty loud as the evening goes on. We really like the sushi there.
We have only eaten at Narcoossee's once, but we didn't care for it. The ambiance was nice, and the service was pretty good from what I remember. The food, IMO, was not so much. Others have had far superior experiences, but our lobsters were rubbery and overcooked, and my mom's fish dish was mediocre as well. I want to repeat here again sometime to see if our first time was a fluke, but my sister (my traveling companion on all Disney trips) has no desire to do so.
Go with your gut after looking at the menus and enjoy! We saw many children at both, so in that respect things will likely be fine.