Honestly, as a child, I remember once asking my dad why Mickey couldn't talk. My dad told me: "Its cause if he talks to you, you'll never stop talking to him." LOL. I always thought that was hilarious.
As another poster said, if the child doesn't ask, then don't mention it. When I met Thumper in January, and I'm 25, he didn't talk but we communicated just fine through body language.
Plus, when we were in line to get a picture with Mickey, the cutest thing ever happened before us: this two-three year old little girl ran up to Mickey and held onto him for dear life. She hugged him and no words needed to be exchanged. I mean this little girl traveled all the way from Germany (I overheard the Mother saying they had been to DLP but the Characters didn't interact with her too much), and here he was giving her all the attention she wanted. And she stayed with him for like 5 minutes straight. And no guest behind us complained, nor did the CMs say ok time to go. They waited patiently. And I could see the look on her face, she was the happiest child on Earth.
So in the end, my point is: talking isn't necessary. Just the body language makes a whole difference in a childs life.