Ta-Da! (da)

"Dada".  This little phrase they keep using....what does it mean?  My father's eyes twinkle almost as bright as mine when I say it, but I can't understand why.  It's a simple disyllabic word, not difficult in the slightest, but they rejoice greatly every time I use it.  My mother not quite as much as my father....if anything I can see a hint of reproach behind her smile...
However, as it brings my father so much joy, I suppose I'll keep saying it, foolish as it sounds. Why don't they want me to SPEAK?  To use real words that mean something?  I don't understand.
"Oh JD, you get used to it.  They expect you to be dumb for the first couple years, and then you hit 2 and WHAM!  They expect perfection - perfect behavior, perfect language, perfect table manners.  Ridiculous thought pattern I know."
Now, now MLS, I don't think you should call Mother and Father ridiculous.  And I don't think they would ever call either of us dumb.  I mean, I know I'm not as old and clever as you are, but I believe Mother and Father are inherently good and wonderful and wise.
"Ahem....of course JD.  Whatever you say."