Dutch photographer Sarah Wong began the ongoing project Inside Out: Portraits of Cross-Gender Children in 2003, photographing children who have changed, or are in the process of changing, their sex because they feel they are a different gender to the one that they were born with.

"The Netherlands has probably the most progressive attitude toward gender variance in the world – transgender kids included," says Wong.

The children in these portraits were among the first to undergo a therapy developed by Peggy Cohen-Kettenis, the founder of Europe’s first clinic for children and adolescents with gender dysphoria, at VU University in Amsterdam.