"Innocence at Its Best" joke

Two babies were sitting in their cribs, when one baby shouted to the other,
"Are you a little girl or a little boy?"
"I don't know," replied the other baby giggling.
"What do you mean, you don't know?" said the first baby.
"I mean I don't know how to tell the difference," was the reply.
"Well, I do," said the first baby chuckling, "I'll climb into your crib and find out."
He carefully maneuvered himself into the other baby's crib, then quickly disappeared beneath the blankets.
After a couple of minutes, he resurfaced with a big grin on his face.
"You're a little girl, and I'm a little boy," he said proudly.
"You're ever so clever," cooed the baby girl, "but how can you tell? "
"It's quite easy really," replied the baby boy,
"You've got pink socks and I've got blue ones."