OOOohhhh let me tell you ... I said the same thing about Marco infact I was almost resigned to the fact I had a beautiful "whistler/clicker" just not a talker and I was ok with that. She is ALMOST 2 yrs (Dec 23rd) and I would say just in the last 2 months all that mumbling and grumbling REALLY really turns into words and phrases. Heck each new word she learns she puts on the end of a phrase. So ... Whatcha doing? Turned into Whatcha doing girl? Turned into Whatcha doing Marco?
Just when you think they arent paying attention to you and you dont have to worry bout what you are saying infront of them, is when they drop the dredded F bomb or something that you said you really wish they hadn't of picked up lol.
So I can relate to your worry, give your baby time, Ive heard it here several times Greys do things in the own time just continue to talk to Felix and include your baby in on all that you are doing. I sing to Marco ALL the time and have since she was a baby. It will happen when Felix is ready!