I have a couple from my niece...
When she was just a wee little bub, old enough to talk and eat some solids but still young enough to have her bum plunked into a high chair, she happened to have some yogurt for lunch one day. Mom and I were just doing our own thing, when abruptly niece looks up from her lunch and announces in a very solemn tone, "It's bwoo-bewwy."
It took us a good long while to stop laughing, and the kid was just looking at us like we were crazy...
Next one: niece was walking by this time. I'm an unapologetic drinker of lots of Pepsi, and I'd just come downstairs to get something for a sinus headache. Niece contemplated me, then walked over to my open pack of Pepsi, fished out a can and handed it to me, proclaiming "Here!" Niece got a fit of giggles and a nice squeezy hug for that one, the silly little thing.
And the last one: this is from...just a couple months ago, actually. Family and I had gathered in my grandfather's city for his funeral when he died, and my dear aunt insisted on taking us out to dinner almost every night as thanks for helping her with planning and whatnot. So we were on the way back to the hotel from dinner - we've got a Kia Sorento right now, so front seats, one middle row and two fold-down jumper seats in the back cargo area. (This is important, I swear.) Dad was driving, sister was up front, Mom and I in the middle and niece in one of the seats in the back, and I was entertaining niece as I was sitting right in front of her. Things got a bit loud, as things are wont to do when kids are involved, and to quiet us down, Mom sternly asked "Who's the six year old here?"
At which point niece raised her hand and shouted, "Ooh! Me! The six year old in the trunk!"
We didn't stop laughing until we were back at the hotel.
(That kid's had so many other good quotes...she's a riot!)
ETA: And here's one from when I was wee. My parents knew a rather...exasperating man, the type who thought he knew it all and wasn't afraid to tell you so, and just generally grated on people's nerves. His name was Andy, and his last name was something you really wouldn't expect a very young child to be able to say properly, so when he met little me for the first time, he asked me "Can you say 'hi, Uncle Andy'?"
Cheeky little me looked him right in the eye and replied, "Hi, Mr. (lastname)."
I hear he was very embarrassed that a baby showed him up.