Y.S.
This is just a suggestion, but before you make him dependant on sign language make sure that he doesn't have a hearing problem. He may not be hearing the words correctly so when he repeats them in a request they don't come out right and you don't understand and he gets frustrated. My #2 son was like that, but I didn't "get it" until he was almost 3. He went to speech therapy and over came the problem before he started school. Check with your doctor or even the local school board--some state provide free hearing test for children under 5. You might also check to see if he is tongue-tied. That is when the lingual fraenulum under tongue is restricted. You might want to check this out. http://members.tripod.com/~Caroline_Bowen/tonguetie.html Good luck and keep in mind that some day he will grow up and you will miss that voice.