For the last year we've smiled at our boy who does not say yes. First he would answer our queries (Are you hungry? Do you need help?) with "OK"; this turned into just "oh", which has been his standard affirmative response since at least the age of 2. By six months ago, though, he had begun answering most questions with a full sentence: Would you like some milk? "I would." Do you want to go outside? "Oh, I do." Can you get your blankie? "I can." Are you cold? "I am." Meanwhile, he would sometimes do the same with negative responses ("I am not, I don't..." but often would just use no. The only time we could get him to say "yes" is by asking "Can you say yes?" We found this awfully amusing and endearing, given his overall command of the language.
He came home yesterday from a weekend at Grandma's and suddenly he is not only answering "yeah" to most questions, but treating me to a barrage of agreement with many statements I make: It's time for your bath. "Yeah, yeah, it is"... I have to say I'm sad to see his formal responses disappear, and I'm realizing yet again just how fast he is growing up.
Here is an unrelated video from a month ago, when Carson was recovering from the chicken pox and before he got his latest haircut that REALLY made him look like a big boy: