WENDY:I shall give you a kiss if you like.

PETER: Thank you. (He holds out his hand.)

WENDY: (aghast) Don’t you know what a kiss is?

PETER. I shall know when you give it me. (Not to hurt his feelings she gives him her thimble.)

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

Peter Pan, Act 1 (1904, pub. 1928)
    (Source)

The original version of this scene (with the girl named Maimie, not Wendy) can be found in Barrie's earlier version of the Peter Pan tale, The Little White Bird, ch. 18 "Peter's Goat" (1902):

She said out of pity for him, "I shall give you a kiss if you like," but though he once knew, he had long forgotten what kisses are, and he replied, "Thank you," and held out his hand, thinking she had offered to put something into it. This was a great shock to her, but she felt she could not explain without shaming him, so with charming delicacy she gave Peter a thimble which happened to be in her pocket, and pretended that it was a kiss.

In Barrie's 1911 novelization of the play, Peter and Wendy, ch. 3 "Come Away, Come Away!" this scene is rendered:

She also said she would give him a kiss if he liked, but Peter did not know what she meant, and he held out his hand expectantly.
“Surely you know what a kiss is?” she asked, aghast.
“I shall know when you give it to me,” he replied stiffly, and not to hurt his feelings she gave him a thimble.