MRS. DARLING: I thought all the fairies were dead.

WENDY: (almost reprovingly) No indeed! Their mothers drop the babies into the Never birds’ nests, all mixed up with the eggs, and the mauve fairies are boys and the white ones are girls, and there are some colours who don’t know what they are.

J. M. Barrie (1860-1937) Scottish novelist and dramatist [James Matthew Barrie]

Peter Pan, Act 5 (1904, pub. 1928)
    (Source)

In Barrie's 1911 novelization, Peter and Wendy, ch. 17 "When Wendy Grew Up," this is rendered:

“I thought all the fairies were dead,” Mrs. Darling said.
“There are always a lot of young ones,” explained Wendy, who was now quite an authority, “because you see when a new baby laughs for the first time a new fairy is born, and as there are always new babies there are always new fairies. They live in nests on the tops of trees; and the mauve ones are boys and the white ones are girls, and the blue ones are just little sillies who are not sure what they are.”