Baby Talk!

Our youngest son is around 2 1/2 years old now.  Like most kids, his first words were " mamamama" and "dadadadada".  However, those are really the only words he will say with any regularity.  I think it may be a stubborn streak or something, because every once in a while he will come out with a full sentence and it blows our minds :).  We do all the normal things that parents do to nudge things along....we patiently try to get him to ask for things instead of just handing them over, we sound out the words for him, read to him...you name it and we try it.   Any ideas how to help this progress??  We never had this problem with our 5 year old.  The little rascal you see below is Stubborn, Stubborn!!!!!!