I had a huge vocabulary as a kid. In fact, I remember one of the most important lessons I learned in Kindergarten was to talk dumb to other kids, because if I used the full breadth of my linguistic capabilities they would neither understand me, nor want to be around me. My parents attributed my vocabulary to never using baby talk with us. I suspect they are right. We never use dumbed down words with our son and here he is, less than two, frequently using words like "concrete mixer" and "delicious". Makes me so proud!