Narcooses is definitely the more family friendly. They dim the lights and play the music for the MK fireworks there, btw. There is no dress code, although I would suggest that a bit more than theme park casual would be appropriate. (Sun dresses or capris for the ladies and chino's and a golf shirt type stuff for the men, but you defnintely don't need more than that
Citrico's does have a dress code: Collared shirt prefered for gentlemen. No tank tops, t-shirts, cut offs or jeans. (This is directly from an e-mail sent to me by the Polynesian concierge)
When we ate there a couple weeks ago, DH wore dress slacks, an oxford shirt and sport coat (no tie), and I was in a linen pant suit. We felt that we were attired just right for the atmosphere there. We didn't see many kids there, and service is relaxed, so it probably wouldn't be the best choice for family dining. My 16 year old DS wouldn't have lasted through dessert...
Have you also given thought to the close by (quick walk) restuarants at the Poly as well? The Kona Cafe is a GREAT family option with excellent food, and the prices there are IMHO reasonable. O'Hana has a interesting menu and character meals.
But if you specifically want a GF restaurant, Narcooses would be a much better choice for a family.
Anne