I too have always spoken with my girls (and any other child for that matter) like they are adults... like their understanding is that of an equal... within reason of course. Their understanding is much greater than any child development book will tell you it is.
When others talk to either of my girls in that baby way... they both have the funniest reactions. Aidan will get really quiet, her forehead creases, she'll look uncomfortable, and then speak very plainly and with an exaggerated enunciation of her words. (Which, in turn, almost always causes the adult to become uncomfortable) With Ainsley, her little face just screws up with a "huh?" expression and she'll turn or walk away from whoever spoke to her like that.
Granted, there are moments when I'll act silly when they're little "I'm gonna get you... I'm gonna get you" but in general I only temper how many details I go into or what words I use.
