You can meet Tiana and Naveen in the parks at WDW. I met Tiana a few weeks ago and had one of my best character interactions with her ever. She was warm, funny, and very charming.
As to why Tiana and Naveen are not at a character meal -- the Moms Panel is not privy to that sort of information. We are not Disney employees, just visitors and fans like you.
I can tell you that Disney welcomes guest feedback and suggestions. You're welcome to contact Disney directly with your ideas. All guest suggestions or comments should be directed to the Guest
Communications Department. They can be reach through the mail at:
Walt Disney World Guest Communications
PO Box 10040
Lake Buena Vista, FL 32830-0040
The e-mail address for Guest Communications is:
wdw.guest.communications@disneyworld.com.
They'll make sure that your suggestion gets into the right hands at Disney World.