My ex-boss told me this years ago.
He mum took his twin daughters (ie: her grand-daughters, for those of you struggling) to the chip shop for some fish and chips.

A couple of places ahead of them in the queue was a black man.

The grandma knew that something was going to happen when one of the girls kept peering at the black guy around her grandma's legs. Finally, she piped up:

"Grandma?"
"Yes dear?" (nervously)
"Why is that man doing an impression of a duck?"

Thankfully, he didn't realise that she meant "why was he fashioning his mouth into the shape of a beak by pushing his lips out"... or if he did he kept quiet about it.
(Professor Kenny Martin Hmm? What?, Tue 22 Apr 2008, 16:00, 2 replies)

My brother (when about 5)
caught sight of the first black man he'd ever seen in real life and asked,

"Mummy, is that man a Minstrel?"

For those of you too young to get this, google Black & White Minstrel Show.
(TheWeeWitch hasn't been here much recently .., Tue 22 Apr 2008, 16:22, closed)

my mate's little brother
was in his pram one day and spotted the first black person he'd ever seen that wasn't in a professional setting. beaming like a loon, he looks up at the man and says "hello, doctor!"
his poor mother didn't know where to put her face.
( Smash Monkey lowering the tone of the whole internet, Tue 22 Apr 2008, 17:17, closed)