Pier 99 is on North Beach near the Aquarium. You could walk there. Blackbeard's is there, too. they are both of the island motif. Burgers, seafood, and on the ocean. Informal and kid-friendly.
My favorite dining spot in CC is Mama Mia's downtown. Great Italian. It's nice but not too formal. Beware, it is not inexpensive and he only takes cash. No credit.
The bar/restaurant at the top of the Omni has a great panaramic view of the city. Pretty after dark and a good place for an after dinner drink. They have good food, not great, and are pricey as you would expect.
There are two Omni's downtown...I'm referring to the one closest to the aquarium.
Water Street is another good place downtown. Good seafood menu and informal. Very popular and I always thought a bit overrated. It is a step up from Landry's though. Reasonably priced.
I was just in CC and ate my one dinner at Mama Mia's but I wouldn't hesitate to eat at any of the above.
Pier 99 may be the place that most suits a family and you can sit outside if there is a table available and look at the Lex. Have fun!