Peek-A-Poo: What's In Your Diaper? (originally titled Mag Ik Eens In Je Luier Kijken?) is a 2010 picture book for children pertaining to toilet training, catered to children of ages two to five, written and illustrated by Guido van Genechten and published by Clavis Publishing on January 1, 2010. It was longlisted for the 2010 Bookseller/Diagram Prize for Oddest Title of the Year. Originally penned in Dutch, the book has been adapted into many languages, including English and Afrikaans.